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Case study research : design and methods

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Case Study Research and Applications: Design and Methods

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This site is intended to enhance your use of  Case Study Research and Applications, Sixth Edition,  by Robert K. Yin. Please note that all the resources on this site are especially geared toward maximizing your understanding of the material. 

Recognized as one of the most cited methodology books in the social sciences, the  Sixth Edition  of Robert K. Yin's bestselling text provides a complete portal to the world of case study research. With the integration of 11 applications in this edition, the book gives readers access to exemplary case studies drawn from a wide variety of academic and applied fields. Ultimately,  Case Study Research and Applications  will guide students in the successful use and application of the case study research method.

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Case Study Research

• First Online: 29 September 2022

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• Robert E. White   ORCID: orcid.org/0000-0002-8045-164X 3 &
• Karyn Cooper 4  

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As a footnote to the previous chapter, there is such a beast known as the ethnographic case study. Ethnographic case study has found its way into this chapter rather than into the previous one because of grammatical considerations. Simply put, the “case study” part of the phrase is the noun (with “case” as an adjective defining what kind of study it is), while the “ethnographic” part of the phrase is an adjective defining the type of case study that is being conducted. As such, the case study becomes the methodology, while the ethnography part refers to a method, mode or approach relating to the development of the study.

The experiential account that we get from a case study or qualitative research of a similar vein is just so necessary. How things happen over time and the degree to which they are subject to personality and how they are only gradually perceived as tolerable or intolerable by the communities and the groups that are involved is so important. Robert Stake, University of Illinois, Urbana-Champaign

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A Case in Case Study Methodology

Christine Benedichte Meyer

Norwegian School of Economics and Business Administration

Meyer, C. B. (2001). A Case in Case Study Methodology. Field Methods 13 (4), 329-352.

The purpose of this article is to provide a comprehensive view of the case study process from the researcher’s perspective, emphasizing methodological considerations. As opposed to other qualitative or quantitative research strategies, such as grounded theory or surveys, there are virtually no specific requirements guiding case research. This is both the strength and the weakness of this approach. It is a strength because it allows tailoring the design and data collection procedures to the research questions. On the other hand, this approach has resulted in many poor case studies, leaving it open to criticism, especially from the quantitative field of research. This article argues that there is a particular need in case studies to be explicit about the methodological choices one makes. This implies discussing the wide range of decisions concerned with design requirements, data collection procedures, data analysis, and validity and reliability. The approach here is to illustrate these decisions through a particular case study of two mergers in the financial industry in Norway.

In the past few years, a number of books have been published that give useful guidance in conducting qualitative studies (Gummesson 1988; Cassell & Symon 1994; Miles & Huberman 1994; Creswell 1998; Flick 1998; Rossman & Rallis 1998; Bryman & Burgess 1999; Marshall & Rossman 1999; Denzin & Lincoln 2000). One approach often mentioned is the case study (Yin 1989). Case studies are widely used in organizational studies in the social science disciplines of sociology, industrial relations, and anthropology (Hartley 1994). Such a study consists of detailed investigation of one or more organizations, or groups within organizations, with a view to providing an analysis of the context and processes involved in the phenomenon under study.

As opposed to other qualitative or quantitative research strategies, such as grounded theory (Glaser and Strauss 1967) or surveys (Nachmias & Nachmias 1981), there are virtually no specific requirements guiding case research. Yin (1989) and Eisenhardt (1989) give useful insights into the case study as a research strategy, but leave most of the design decisions on the table. This is both the strength and the weakness of this approach. It is a strength because it allows tailoring the design and data collection procedures to the research questions. On the other hand, this approach has resulted in many poor case studies, leaving it open to criticism, especially from the quantitative field of research (Cook and Campbell 1979). The fact that the case study is a rather loose design implies that there are a number of choices that need to be addressed in a principled way.

Although case studies have become a common research strategy, the scope of methodology sections in articles published in journals is far too limited to give the readers a detailed and comprehensive view of the decisions taken in the particular studies, and, given the format of methodology sections, will remain so. The few books (Yin 1989, 1993; Hamel, Dufour, & Fortin 1993; Stake 1995) and book chapters on case studies (Hartley 1994; Silverman 2000) are, on the other hand, mainly normative and span a broad range of different kinds of case studies. One exception is Pettigrew (1990, 1992), who places the case study in the context of a research tradition (the Warwick process research).

Given the contextual nature of the case study and its strength in addressing contemporary phenomena in real-life contexts, I believe that there is a need for articles that provide a comprehensive overview of the case study process from the researcher’s perspective, emphasizing methodological considerations. This implies addressing the whole range of choices concerning specific design requirements, data collection procedures, data analysis, and validity and reliability.

WHY A CASE STUDY?

Case studies are tailor-made for exploring new processes or behaviors or ones that are little understood (Hartley 1994). Hence, the approach is particularly useful for responding to how and why questions about a contemporary set of events (Leonard-Barton 1990). Moreover, researchers have argued that certain kinds of information can be difficult or even impossible to tackle by means other than qualitative approaches such as the case study (Sykes 1990). Gummesson (1988:76) argues that an important advantage of case study research is the opportunity for a holistic view of the process: “The detailed observations entailed in the case study method enable us to study many different aspects, examine them in relation to each other, view the process within its total environment and also use the researchers’ capacity for ‘verstehen.’ ”

The contextual nature of the case study is illustrated in Yin’s (1993:59) definition of a case study as an empirical inquiry that “investigates a contemporary phenomenon within its real-life context and addresses a situation in which the boundaries between phenomenon and context are not clearly evident.”

The key difference between the case study and other qualitative designs such as grounded theory and ethnography (Glaser & Strauss 1967; Strauss & Corbin 1990; Gioia & Chittipeddi 1991) is that the case study is open to the use of theory or conceptual categories that guide the research and analysis of data. In contrast, grounded theory or ethnography presupposes that theoretical perspectives are grounded in and emerge from firsthand data. Hartley (1994) argues that without a theoretical framework, the researcher is in severe danger of providing description without meaning. Gummesson (1988) says that a lack of preunderstanding will cause the researcher to spend considerable time gathering basic information. This preunderstanding may arise from general knowledge such as theories, models, and concepts or from specific knowledge of institutional conditions and social patterns. According to Gummesson, the key is not to require researchers to have split but dual personalities: “Those who are able to balance on a razor’s edge using their pre-understanding without being its slave” (p. 58).

DESCRIPTION OF THE ILLUSTRATIVE STUDY

The study that will be used for illustrative purposes is a comparative and longitudinal case study of organizational integration in mergers and acquisitions taking place in Norway. The study had two purposes: (1) to identify contextual factors and features of integration that facilitated or impeded organizational integration, and (2) to study how the three dimensions of organizational integration (integration of tasks, unification of power, and integration of cultures and identities) interrelated and evolved over time. Examples of contextual factors were relative power, degree of friendliness, and economic climate. Integration features included factors such as participation, communication, and allocation of positions and functions.

Mergers and acquisitions are inherently complex. Researchers in the field have suggested that managers continuously underestimate the task of integrating the merging organizations in the postintegration process (Haspeslaph & Jemison 1991). The process of organizational integration can lead to sharp interorganizational conflict as the different top management styles, organizational and work unit cultures, systems, and other aspects of organizational life come into contact (Blake & Mounton 1985; Schweiger & Walsh 1990; Cartwright & Cooper 1993). Furthermore, cultural change in mergers and acquisitions is compounded by additional uncertainties, ambiguities, and stress inherent in the combination process (Buono & Bowditch 1989).

I focused on two combinations: one merger and one acquisition. The first case was a merger between two major Norwegian banks, Bergen Bank and DnC (to be named DnB), that started in the late 1980s. The second case was a study of a major acquisition in the insurance industry (i.e., Gjensidige’s acquisition of Forenede), that started in the early 1990s. Both combinations aimed to realize operational synergies though merging the two organizations into one entity. This implied disruption of organizational boundaries and threat to the existing power distribution and organizational cultures.

The study of integration processes in mergers and acquisitions illustrates the need to find a design that opens for exploration of sensitive issues such as power struggles between the two merging organizations. Furthermore, the inherent complexity in the integration process, involving integration of tasks, unification of power, and cultural integration stressed the need for in-depth study of the phenomenon over time. To understand the cultural integration process, the design also had to be linked to the past history of the two organizations.

DESIGN DECISIONS

In the introduction, I stressed that a case is a rather loose design that requires that a number of design choices be made. In this section, I go through the most important choices I faced in the study of organizational integration in mergers and acquisitions. These include: (1) selection of cases; (2) sampling time; (3) choosing business areas, divisions, and sites; and (4) selection of and choices regarding data collection procedures, interviews, documents, and observation.

Selection of Cases

There are several choices involved in selecting cases. First, there is the question of how many cases to include. Second, one must sample cases and decide on a unit of analysis. I will explore these issues subsequently.

Single or Multiple Cases

Case studies can involve single or multiple cases. The problem of single cases is limitations in generalizability and several information-processing biases (Eisenhardt 1989).

One way to respond to these biases is by applying a multi-case approach (Leonard-Barton 1990). Multiple cases augment external validity and help guard against observer biases. Moreover, multi-case sampling adds confidence to findings. By looking at a range of similar and contrasting cases, we can understand a single-case finding, grounding it by specifying how and where and, if possible, why it behaves as it does. (Miles & Huberman 1994)

Given these limitations of the single case study, it is desirable to include more than one case study in the study. However, the desire for depth and a pluralist perspective and tracking the cases over time implies that the number of cases must be fairly few. I chose two cases, which clearly does not support generalizability any more than does one case, but allows for comparison and contrast between the cases as well as a deeper and richer look at each case.

Originally, I planned to include a third case in the study. Due to changes in management during the initial integration process, my access to the case was limited and I left this case entirely. However, a positive side effect was that it allowed a deeper investigation of the two original cases and in hindsight turned out to be a good decision.

Sampling Cases

The logic of sampling cases is fundamentally different from statistical sampling. The logic in case studies involves theoretical sampling, in which the goal is to choose cases that are likely to replicate or extend the emergent theory or to fill theoretical categories and provide examples for polar types (Eisenhardt 1989). Hence, whereas quantitative sampling concerns itself with representativeness, qualitative sampling seeks information richness and selects the cases purposefully rather than randomly (Crabtree and Miller 1992).

The choice of cases was guided by George (1979) and Pettigrew’s (1990) recommendations. The aim was to find cases that matched the three dimensions in the dependent variable and provided variation in the contextual factors, thus representing polar cases.

To match the choice of outcome variable, organizational integration, I chose cases in which the purpose was to fully consolidate the merging parties’ operations. A full consolidation would imply considerable disruption in the organizational boundaries and would be expected to affect the task-related, political, and cultural features of the organizations. As for the contextual factors, the two cases varied in contextual factors such as relative power, friendliness, and economic climate. The DnB merger was a friendly combination between two equal partners in an unfriendly economic climate. Gjensidige’s acquisition of Forenede was, in contrast, an unfriendly and unbalanced acquisition in a friendly economic climate.

Unit of Analysis

Another way to respond to researchers’ and respondents’ biases is to have more than one unit of analysis in each case (Yin 1993). This implies that, in addition to developing contrasts between the cases, researchers can focus on contrasts within the cases (Hartley 1994). In case studies, there is a choice of a holistic or embedded design (Yin 1989). A holistic design examines the global nature of the phenomenon, whereas an embedded design also pays attention to subunit(s).

I used an embedded design to analyze the cases (i.e., within each case, I also gave attention to subunits and subprocesses). In both cases, I compared the combination processes in the various divisions and local networks. Moreover, I compared three distinct change processes in DnB: before the merger, during the initial combination, and two years after the merger. The overall and most important unit of analysis in the two cases was, however, the integration process.

Sampling Time

According to Pettigrew (1990), time sets a reference for what changes can be seen and how those changes are explained. When conducting a case study, there are several important issues to decide when sampling time. The first regards how many times data should be collected, while the second concerns when to enter the organizations. There is also a need to decide whether to collect data on a continuous basis or in distinct periods.

Number of data collections. I studied the process by collecting real time and retrospective data at two points in time, with one-and-a-half- and two-year intervals in the two cases. Collecting data twice had some interesting implications for the interpretations of the data. During the first data collection in the DnB study, for example, I collected retrospective data about the premerger and initial combination phase and real-time data about the second step in the combination process.

Although I gained a picture of how the employees experienced the second stage of the combination process, it was too early to assess the effects of this process at that stage. I entered the organization two years later and found interesting effects that I had not anticipated the first time. Moreover, it was interesting to observe how people’s attitudes toward the merger processes changed over time to be more positive and less emotional.

When to enter the organizations. It would be desirable to have had the opportunity to collect data in the precombination processes. However, researchers are rarely given access in this period due to secrecy. The emphasis in this study was to focus on the postcombination process. As such, the precombination events were classified as contextual factors. This implied that it was most important to collect real-time data after the parties had been given government approval to merge or acquire. What would have been desirable was to gain access earlier in the postcombination process. This was not possible because access had to be negotiated. Due to the change of CEO in the middle of the merger process and the need for renegotiating access, this took longer than expected.

Regarding the second case, I was restricted by the time frame of the study. In essence, I had to choose between entering the combination process as soon as governmental approval was given, or entering the organization at a later stage. In light of the previous studies in the field that have failed to go beyond the initial two years, and given the need to collect data about the cultural integration process, I chose the latter strategy. And I decided to enter the organizations at two distinct periods of time rather than on a continuous basis.

There were several reasons for this approach, some methodological and some practical. First, data collection on a continuous basis would have required use of extensive observation that I didn’t have access to, and getting access to two data collections in DnB was difficult in itself. Second, I had a stay abroad between the first and second data collection in Gjensidige. Collecting data on a continuous basis would probably have allowed for better mapping of the ongoing integration process, but the contrasts between the two different stages in the integration process that I wanted to elaborate would probably be more difficult to detect. In Table 1 I have listed the periods of time in which I collected data in the two combinations.

Sampling Business Areas, Divisions, and Sites

Even when the cases for a study have been chosen, it is often necessary to make further choices within each case to make the cases researchable. The most important criteria that set the boundaries for the study are importance or criticality, relevance, and representativeness. At the time of the data collection, my criteria for making these decisions were not as conscious as they may appear here. Rather, being restricted by time and my own capacity as a researcher, I had to limit the sites and act instinctively. In both cases, I decided to concentrate on the core businesses (criticality criterion) and left out the business units that were only mildly affected by the integration process (relevance criterion). In the choice of regional offices, I used the representativeness criterion as the number of offices widely exceeded the number of sites possible to study. In making these choices, I relied on key informants in the organizations.

SELECTION OF DATA COLLECTION PROCEDURES

The choice of data collection procedures should be guided by the research question and the choice of design. The case study approach typically combines data collection methods such as archives, interviews, questionnaires, and observations (Yin 1989). This triangulated methodology provides stronger substantiation of constructs and hypotheses. However, the choice of data collection methods is also subject to constraints in time, financial resources, and access.

I chose a combination of interviews, archives, and observation, with main emphasis on the first two. Conducting a survey was inappropriate due to the lack of established concepts and indicators. The reason for limited observation, on the other hand, was due to problems in obtaining access early in the study and time and resource constraints. In addition to choosing among several different data collection methods, there are a number of choices to be made for each individual method.

When relying on interviews as the primary data collection method, the issue of building trust between the researcher and the interviewees becomes very important. I addressed this issue by several means. First, I established a procedure of how to approach the interviewees. In most cases, I called them first, then sent out a letter explaining the key features of the project and outlining the broad issues to be addressed in the interview. In this letter, the support from the institution’s top management was also communicated. In most cases, the top management’s support of the project was an important prerequisite for the respondent’s input. Some interviewees did, however, fear that their input would be open to the top management without disguising the information source. Hence, it became important to communicate how I intended to use and store the information.

To establish trust, I also actively used my preunderstanding of the context in the first case and the phenomenon in the second case. As I built up an understanding of the cases, I used this information to gain confidence. The active use of my preunderstanding did, however, pose important challenges in not revealing too much of the research hypotheses and in balancing between asking open-ended questions and appearing knowledgeable.

There are two choices involved in conducting interviews. The first concerns the sampling of interviewees. The second is that you must decide on issues such as the structure of the interviews, use of tape recorder, and involvement of other researchers.

Sampling Interviewees

Following the desire for detailed knowledge of each case and for grasping different participant’s views the aim was, in line with Pettigrew (1990), to apply a pluralist view by describing and analyzing competing versions of reality as seen by actors in the combination processes.

I used four criteria for sampling informants. First, I drew informants from populations representing multiple perspectives. The first data collection in DnB was primarily focused on the top management level. Moreover, most middle managers in the first data collection were employed at the head offices, either in Bergen or Oslo. In the second data collection, I compensated for this skew by including eight local middle managers in the sample. The difference between the number of employees interviewed in DnB and Gjensidige was primarily due to the fact that Gjensidige has three unions, whereas DnB only has one. The distribution of interviewees is outlined in Table 2 .

The second criterion was to use multiple informants. According to Glick et al. (1990), an important advantage of using multiple informants is that the validity of information provided by one informant can be checked against that provided by other informants. Moreover, the validity of the data used by the researcher can be enhanced by resolving the discrepancies among different informants’ reports. Hence, I selected multiple respondents from each perspective.

Third, I focused on key informants who were expected to be knowledgeable about the combination process. These people included top management members, managers, and employees involved in the integration project. To validate the information from these informants, I also used a fourth criterion by selecting managers and employees who had been affected by the process but who were not involved in the project groups.

Structured versus unstructured. In line with the explorative nature of the study, the goal of the interviews was to see the research topic from the perspective of the interviewee, and to understand why he or she came to have this particular perspective. To meet this goal, King (1994:15) recommends that one have “a low degree of structure imposed on the interviewer, a preponderance of open questions, a focus on specific situations and action sequences in the world of the interviewee rather than abstractions and general opinions.” In line with these recommendations, the collection of primary data in this study consists of unstructured interviews.

Using tape recorders and involving other researchers. The majority of the interviews were tape-recorded, and I could thus concentrate fully on asking questions and responding to the interviewees’ answers. In the few interviews that were not tape-recorded, most of which were conducted in the first phase of the DnB-study, two researchers were present. This was useful as we were both able to discuss the interviews later and had feedback on the role of an interviewer.

In hindsight, however, I wish that these interviews had been tape-recorded to maintain the level of accuracy and richness of data. Hence, in the next phases of data collection, I tape-recorded all interviews, with two exceptions (people who strongly opposed the use of this device). All interviews that were tape-recorded were transcribed by me in full, which gave me closeness and a good grasp of the data.

When organizations merge or make acquisitions, there are often a vast number of documents to choose from to build up an understanding of what has happened and to use in the analyses. Furthermore, when firms make acquisitions or merge, they often hire external consultants, each of whom produces more documents. Due to time constraints, it is seldom possible to collect and analyze all these documents, and thus the researcher has to make a selection.

The choice of documentation was guided by my previous experience with merger and acquisition processes and the research question. Hence, obtaining information on the postintegration process was more important than gaining access to the due-diligence analysis. As I learned about the process, I obtained more documents on specific issues. I did not, however, gain access to all the documents I asked for, and, in some cases, documents had been lost or shredded.

The documents were helpful in a number of ways. First, and most important, they were used as inputs to the interview guide and saved me time, because I did not have to ask for facts in the interviews. They were also useful for tracing the history of the organizations and statements made by key people in the organizations. Third, the documents were helpful in counteracting the biases of the interviews. A list of the documents used in writing the cases is shown in Table 3 .

Observation

The major strength of direct observation is that it is unobtrusive and does not require direct interaction with participants (Adler and Adler 1994). Observation produces rigor when it is combined with other methods. When the researcher has access to group processes, direct observation can illuminate the discrepancies between what people said in the interviews and casual conversations and what they actually do (Pettigrew 1990).

As with interviews, there are a number of choices involved in conducting observations. Although I did some observations in the study, I used interviews as the key data collection source. Discussion in this article about observations will thus be somewhat limited. Nevertheless, I faced a number of choices in conducting observations, including type of observation, when to enter, how much observation to conduct, and which groups to observe.

The are four ways in which an observer may gather data: (1) the complete participant who operates covertly, concealing any intention to observe the setting; (2) the participant-as-observer, who forms relationships and participates in activities, but makes no secret of his or her intentions to observe events; (3) the observer-as-participant, who maintains only superficial contact with the people being studied; and (4) the complete observer, who merely stands back and eavesdrops on the proceedings (Waddington 1994).

In this study, I used the second and third ways of observing. The use of the participant-as-observer mode, on which much ethnographic research is based, was rather limited in the study. There were two reasons for this. First, I had limited time available for collecting data, and in my view interviews made more effective use of this limited time than extensive participant observation. Second, people were rather reluctant to let me observe these political and sensitive processes until they knew me better and felt I could be trusted. Indeed, I was dependent on starting the data collection before having built sufficient trust to observe key groups in the integration process. Nevertheless, Gjensidige allowed me to study two employee seminars to acquaint me with the organization. Here I admitted my role as an observer but participated fully in the activities. To achieve variation, I chose two seminars representing polar groups of employees.

As observer-as-participant, I attended a top management meeting at the end of the first data collection in Gjensidige and observed the respondents during interviews and in more informal meetings, such as lunches. All these observations gave me an opportunity to validate the data from the interviews. Observing the top management group was by far the most interesting and rewarding in terms of input.

Both DnB and Gjensidige started to open up for more extensive observation when I was about to finish the data collection. By then, I had built up the trust needed to undertake this approach. Unfortunately, this came a little late for me to take advantage of it.

DATA ANALYSIS

Published studies generally describe research sites and data-collection methods, but give little space to discuss the analysis (Eisenhardt 1989). Thus, one cannot follow how a researcher arrives at the final conclusions from a large volume of field notes (Miles and Huberman 1994).

In this study, I went through the stages by which the data were reduced and analyzed. This involved establishing the chronology, coding, writing up the data according to phases and themes, introducing organizational integration into the analysis, comparing the cases, and applying the theory. I will discuss these phases accordingly.

The first step in the analysis was to establish the chronology of the cases. To do this, I used internal and external documents. I wrote the chronologies up and included appendices in the final report.

The next step was to code the data into phases and themes reflecting the contextual factors and features of integration. For the interviews, this implied marking the text with a specific phase and a theme, and grouping the paragraphs on the same theme and phase together. I followed the same procedure in organizing the documents.

I then wrote up the cases using phases and themes to structure them. Before starting to write up the cases, I scanned the information on each theme, built up the facts and filled in with perceptions and reactions that were illustrative and representative of the data.

The documents were primarily useful in establishing the facts, but they also provided me with some perceptions and reactions that were validated in the interviews. The documents used included internal letters and newsletters as well as articles from the press. The interviews were less factual, as intended, and gave me input to assess perceptions and reactions. The limited observation was useful to validate the data from the interviews. The result of this step was two descriptive cases.

To make each case more analytical, I introduced the three dimensions of organizational integration—integration of tasks, unification of power, and cultural integration—into the analysis. This helped to focus the case and to develop a framework that could be used to compare the cases. The cases were thus structured according to phases, organizational integration, and themes reflecting the factors and features in the study.

I took all these steps to become more familiar with each case as an individual entity. According to Eisenhardt (1989:540), this is a process that “allows the unique patterns of each case to emerge before the investigators push to generalise patterns across cases. In addition it gives investigators a rich familiarity with each case which, in turn, accelerates cross-case comparison.”

The comparison between the cases constituted the next step in the analysis. Here, I used the categories from the case chapters, filled in the features and factors, and compared and contrasted the findings. The idea behind cross-case searching tactics is to force investigators to go beyond initial impressions, especially through the use of structural and diverse lenses on the data. These tactics improve the likelihood of accurate and reliable theory, that is, theory with a close fit to the data (Eisenhardt 1989).

As a result, I had a number of overall themes, concepts, and relationships that had emerged from the within-case analysis and cross-case comparisons. The next step was to compare these emergent findings with theory from the organizational field of mergers and acquisitions, as well as other relevant perspectives.

This method of generalization is known as analytical generalization. In this approach, a previously developed theory is used as a template with which to compare the empirical results of the case study (Yin 1989). This comparison of emergent concepts, theory, or hypotheses with the extant literature involves asking what it is similar to, what it contradicts, and why. The key to this process is to consider a broad range of theory (Eisenhardt 1989). On the whole, linking emergent theory to existent literature enhances the internal validity, generalizability, and theoretical level of theory-building from case research.

According to Eisenhardt (1989), examining literature that conflicts with the emergent literature is important for two reasons. First, the chance of neglecting conflicting findings is reduced. Second, “conflicting results forces researchers into a more creative, frame-breaking mode of thinking than they might otherwise be able to achieve” (p. 544). Similarly, Eisenhardt (1989) claims that literature discussing similar findings is important because it ties together underlying similarities in phenomena not normally associated with each other. The result is often a theory with a stronger internal validity, wider generalizability, and a higher conceptual level.

The analytical generalization in the study included exploring and developing the concepts and examining the relationships between the constructs. In carrying out this analytical generalization, I acted on Eisenhardt’s (1989) recommendation to use a broad range of theory. First, I compared and contrasted the findings with the organizational stream on mergers and acquisition literature. Then I discussed other relevant literatures, including strategic change, power and politics, social justice, and social identity theory to explore how these perspectives could contribute to the understanding of the findings. Finally, I discussed the findings that could not be explained either by the merger and acquisition literature or the four theoretical perspectives.

In every scientific study, questions are raised about whether the study is valid and reliable. The issues of validity and reliability in case studies are just as important as for more deductive designs, but the application is fundamentally different.

VALIDITY AND RELIABILITY

The problems of validity in qualitative studies are related to the fact that most qualitative researchers work alone in the field, they focus on the findings rather than describe how the results were reached, and they are limited in processing information (Miles and Huberman 1994).

Researchers writing about qualitative methods have questioned whether the same criteria can be used for qualitative and quantitative studies (Kirk & Miller 1986; Sykes 1990; Maxwell 1992). The problem with the validity criteria suggested in qualitative research is that there is little consistency across the articles as each author suggests a new set of criteria.

One approach in examining validity and reliability is to apply the criteria used in quantitative research. Hence, the criteria to be examined here are objectivity/intersubjectivity, construct validity, internal validity, external validity, and reliability.

Objectivity/Intersubjectivity

The basic issue of objectivity can be framed as one of relative neutrality and reasonable freedom from unacknowledged research biases (Miles & Huberman 1994). In a real-time longitudinal study, the researcher is in danger of losing objectivity and of becoming too involved with the organization, the people, and the process. Hence, Leonard-Barton (1990) claims that one may be perceived as, and may even become, an advocate rather than an observer.

According to King (1994), however, qualitative research, in seeking to describe and make sense of the world, does not require researchers to strive for objectivity and distance themselves from research participants. Indeed, to do so would make good qualitative research impossible, as the interviewer’s sensitivity to subjective aspects of his or her relationship with the interviewee is an essential part of the research process (King 1994:31).

This does not imply, however, that the issue of possible research bias can be ignored. It is just as important as in a structured quantitative interview that the findings are not simply the product of the researcher’s prejudices and prior experience. One way to guard against this bias is for the researcher to explicitly recognize his or her presuppositions and to make a conscious effort to set these aside in the analysis (Gummesson 1988). Furthermore, rival conclusions should be considered (Miles & Huberman 1994).

My experience from the first phase of the DnB study was that it was difficult to focus the questions and the analysis of the data when the research questions were too vague and broad. As such, developing a framework before collecting the data for the study was useful in guiding the collection and analysis of data. Nevertheless, it was important to be open-minded and receptive to new and surprising data. In the DnB study, for example, the positive effect of the reorganization process on the integration of cultures came as a complete surprise to me and thus needed further elaboration.

I also consciously searched for negative evidence and problems by interviewing outliers (Miles & Huberman 1994) and asking problem-oriented questions. In Gjensidige, the first interviews with the top management revealed a much more positive perception of the cultural integration process than I had expected. To explore whether this was a result of overreliance on elite informants, I continued posing problem-oriented questions to outliers and people at lower levels in the organization. Moreover, I told them about the DnB study to be explicit about my presuppositions.

Another important issue when assessing objectivity is whether other researchers can trace the interpretations made in the case studies, or what is called intersubjectivity. To deal with this issue, Miles & Huberman (1994) suggest that: (1) the study’s general methods and procedures should be described in detail, (2) one should be able to follow the process of analysis, (3) conclusions should be explicitly linked with exhibits of displayed data, and (4) the data from the study should be made available for reanalysis by others.

In response to these requirements, I described the study’s data collection procedures and processing in detail. Then, the primary data were displayed in the written report in the form of quotations and extracts from documents to support and illustrate the interpretations of the data. Because the study was written up in English, I included the Norwegian text in a separate appendix. Finally, all the primary data from the study were accessible for a small group of distinguished researchers.

Construct Validity

Construct validity refers to whether there is substantial evidence that the theoretical paradigm correctly corresponds to observation (Kirk & Miller 1986). In this form of validity, the issue is the legitimacy of the application of a given concept or theory to established facts.

The strength of qualitative research lies in the flexible and responsive interaction between the interviewer and the respondents (Sykes 1990). Thus, meaning can be probed, topics covered easily from a number of angles, and questions made clear for respondents. This is an advantage for exploring the concepts (construct or theoretical validity) and the relationships between them (internal validity). Similarly, Hakim (1987) says the great strength of qualitative research is the validity of data obtained because individuals are interviewed in sufficient detail for the results to be taken as true, correct, and believable reports of their views and experiences.

Construct validity can be strengthened by applying a longitudinal multicase approach, triangulation, and use of feedback loops. The advantage of applying a longitudinal approach is that one gets the opportunity to test sensitivity of construct measures to the passage of time. Leonard-Barton (1990), for example, found that one of her main constructs, communicability, varied across time and relative to different groups of users. Thus, the longitudinal study aided in defining the construct more precisely. By using more than one case study, one can validate stability of construct across situations (Leonard-Barton 1990). Since my study only consists of two case studies, the opportunity to test stability of constructs across cases is somewhat limited. However, the use of more than one unit of analysis helps to overcome this limitation.

Construct validity is strengthened by the use of multiple sources of evidence to build construct measures, which define the construct and distinguish it from other constructs. These multiple sources of evidence can include multiple viewpoints within and across the data sources. My study responds to these requirements in its sampling of interviewees and uses of multiple data sources.

Use of feedback loops implies returning to interviewees with interpretations and developing theory and actively seeking contradictions in data (Crabtree & Miller 1992; King 1994). In DnB, the written report had to be approved by the bank’s top management after the first data collection. Apart from one minor correction, the bank had no objections to the established facts. In their comments on my analysis, some of the top managers expressed the view that the political process had been overemphasized, and that the CEO’s role in initiating a strategic process was undervalued. Hence, an important objective in the second data collection was to explore these comments further. Moreover, the report was not as positive as the management had hoped for, and negotiations had to be conducted to publish the report. The result of these negotiations was that publication of the report was postponed one-and-a-half years.

The experiences from the first data collection in the DnB had some consequences. I was more cautious and brought up the problems of confidentiality and the need to publish at the outset of the Gjensidige study. Also, I had to struggle to get access to the DnB case for the second data collection and some of the information I asked for was not released. At Gjensidige, I sent a preliminary draft of the case chapter to the corporation’s top management for comments, in addition to having second interviews with a small number of people. Beside testing out the factual description, these sessions gave me the opportunity to test out the theoretical categories established as a result of the within-case analysis.

Internal Validity

Internal validity concerns the validity of the postulated relationships among the concepts. The main problem of internal validity as a criterion in qualitative research is that it is often not open to scrutiny. According to Sykes (1990), the researcher can always provide a plausible account and, with careful editing, may ensure its coherence. Recognition of this problem has led to calls for better documentation of the processes of data collection, the data itself, and the interpretative contribution of the researcher. The discussion of how I met these requirements was outlined in the section on objectivity/subjectivity above.

However, there are some advantages in using qualitative methods, too. First, the flexible and responsive methods of data collection allow cross-checking and amplification of information from individual units as it is generated. Respondents’ opinions and understandings can be thoroughly explored. The internal validity results from strategies that eliminate ambiguity and contradiction, filling in detail and establishing strong connections in data.

Second, the longitudinal study enables one to track cause and effect. Moreover, it can make one aware of intervening variables (Leonard-Barton 1990). Eisenhardt (1989:542) states, “Just as hypothesis testing research an apparent relationship may simply be a spurious correlation or may reflect the impact of some third variable on each of the other two. Therefore, it is important to discover the underlying reasons for why the relationship exists.”

Generalizability

According to Mitchell (1983), case studies are not based on statistical inference. Quite the contrary, the inferring process turns exclusively on the theoretically necessary links among the features in the case study. The validity of the extrapolation depends not on the typicality or representativeness of the case but on the cogency of the theoretical reasoning. Hartley (1994:225) claims, “The detailed knowledge of the organization and especially the knowledge about the processes underlying the behaviour and its context can help to specify the conditions under which behaviour can be expected to occur. In other words, the generalisation is about theoretical propositions not about populations.”

Generalizability is normally based on the assumption that this theory may be useful in making sense of similar persons or situations (Maxwell 1992). One way to increase the generalizability is to apply a multicase approach (Leonard-Barton 1990). The advantage of this approach is that one can replicate the findings from one case study to another. This replication logic is similar to that used on multiple experiments (Yin 1993).

Given the choice of two case studies, the generalizability criterion is not supported in this study. Through the discussion of my choices, I have tried to show that I had to strike a balance between the need for depth and mapping changes over time and the number of cases. In doing so, I deliberately chose to provide a deeper and richer look at each case, allowing the reader to make judgments about the applicability rather than making a case for generalizability.

Reliability

Reliability focuses on whether the process of the study is consistent and reasonably stable over time and across researchers and methods (Miles & Huberman 1994). In the context of qualitative research, reliability is concerned with two questions (Sykes 1990): Could the same study carried out by two researchers produce the same findings? and Could a study be repeated using the same researcher and respondents to yield the same findings?

The problem of reliability in qualitative research is that differences between replicated studies using different researchers are to be expected. However, while it may not be surprising that different researchers generate different findings and reach different conclusions, controlling for reliability may still be relevant. Kirk and Miller’s (1986:311) definition takes into account the particular relationship between the researcher’s orientation, the generation of data, and its interpretation:

For reliability to be calculated, it is incumbent on the scientific investigator to document his or her procedure. This must be accomplished at such a level of abstraction that the loci of decisions internal to the project are made apparent. The curious public deserves to know how the qualitative researcher prepares him or herself for the endeavour, and how the data is collected and analysed.

The study addresses these requirements by discussing my point of departure regarding experience and framework, the sampling and data collection procedures, and data analysis.

Case studies often lack academic rigor and are, as such, regarded as inferior to more rigorous methods where there are more specific guidelines for collecting and analyzing data. These criticisms stress that there is a need to be very explicit about the choices one makes and the need to justify them.

One reason why case studies are criticized may be that researchers disagree about the definition and the purpose of carrying out case studies. Case studies have been regarded as a design (Cook and Campbell 1979), as a qualitative methodology (Cassell and Symon 1994), as a particular data collection procedure (Andersen 1997), and as a research strategy (Yin 1989). Furthermore, the purpose for carrying out case studies is unclear. Some regard case studies as supplements to more rigorous qualitative studies to be carried out in the early stage of the research process; others claim that it can be used for multiple purposes and as a research strategy in its own right (Gummesson 1988; Yin 1989). Given this unclear status, researchers need to be very clear about their interpretation of the case study and the purpose of carrying out the study.

This article has taken Yin’s (1989) definition of the case study as a research strategy as a starting point and argued that the choice of the case study should be guided by the research question(s). In the illustrative study, I used a case study strategy because of a need to explore sensitive, ill-defined concepts in depth, over time, taking into account the context and history of the mergers and the existing knowledge about the phenomenon. However, the choice of a case study strategy extended rather than limited the number of decisions to be made. In Schramm’s (1971, cited in Yin 1989:22–23) words, “The essence of a case study, the central tendency among all types of case study, is that it tries to illuminate a decision or set of decisions, why they were taken, how they were implemented, and with what result.”

Hence, the purpose of this article has been to illustrate the wide range of decisions that need to be made in the context of a particular case study and to discuss the methodological considerations linked to these decisions. I argue that there is a particular need in case studies to be explicit about the methodological choices one makes and that these choices can be best illustrated through a case study of the case study strategy.

As in all case studies, however, there are limitations to the generalizability of using one particular case study for illustrative purposes. As such, the strength of linking the methodological considerations to a specific context and phenomenon also becomes a weakness. However, I would argue that the questions raised in this article are applicable to many case studies, but that the answers are very likely to vary. The design choices are shown in Table 4 . Hence, researchers choosing a longitudinal, comparative case study need to address the same set of questions with regard to design, data collection procedures, and analysis, but they are likely to come up with other conclusions, given their different research questions.

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Christine Benedichte Meyer is an associate professor in the Department of Strategy and Management in the Norwegian School of Economics and Business Administration, Bergen-Sandviken, Norway. Her research interests are mergers and acquisitions, strategic change, and qualitative research. Recent publications include: “Allocation Processes in Mergers and Acquisitions: An Organisational Justice Perspective” (British Journal of Management 2001) and “Motives for Acquisitions in the Norwegian Financial Industry” (CEMS Business Review 1997).

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Case Study Research and Applications Design and Methods

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Recognized as one of the most cited methodology books in the social sciences, the Sixth Edition of Robert K. Yin's bestselling text provides a complete portal to the world of case study research. With the integration of 11 applications in this edition, the book gives readers access to exemplary case studies drawn from a wide variety of academic and applied fields. Ultimately, Case Study Research and Applications will guide students in the successful use and application of the case study research method.

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“The book is filled with tips to the researcher on how to master the craft of doing research overall and specifically how to account for multi-layered cases.”

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Very good introduction to Case Study design. I have used case study approach for my PhD study. I would recommend this book for an indepth understanding of case study design for research projects.

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The book is a really good introduction to case study research and is full of useful examples. I will recommend as the definitive source for students interested in pursuing this further in their projects.

In our Doctor of Ministerial Leadership (DML), Case Study is the Methodology that is required in this program. Robert Yin's book provides the foundational knowledge needed to conduct research using his Case Study design.

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Case Study Research: Design and Methods, 3rd Edition (Applied Social Research Methods, Vol. 5) 3rd Edition

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This new edition of the best-selling Case Study Research has been carefully revised, updated, and expanded while retaining virtually all of the features and coverage of the Second Edition . Robert Yin′s comprehensive presentation covers all aspects of the case study method--from problem definition, design, and data collection, to data analysis and composition and reporting. Yin also traces the uses and importance of case studies to a wide range of disciplines, from sociology, psychology and history to management, planning, social work, and education.

• ISBN-10 0761925538
• ISBN-13 978-0761925538
• Edition 3rd
• Publisher SAGE Publications, Inc
• Publication date December 24, 2002
• Language English
• Dimensions 5.5 x 0.5 x 8.5 inches
• Print length 200 pages
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About the author.

Robert K. Yin is President of COSMOS Corporation, an applied research and social science firm.  Over the years, COSMOS has successfully completed hundreds of projects for federal agencies, state and local agencies, and private foundations.

Outside of COSMOS, Dr. Yin has assisted numerous other research groups, helping to train their field teams or to design research studies. The most recent such engagements have been with The World Bank, the Division of Special Education and disAbility Research at George Mason University, the Department of Nursing Research and Quality Outcomes at the Children’s National Health System (Washington, DC), and the School of Education, Southern New Hampshire University.

Dr. Yin has authored over 100 publications, including authoring or editing 11 books (not counting the multiple editions of any given book). Earlier editions of the present book have been translated into eight languages (Chinese, Japanese, Korean, Swedish, Romanian, Italian, Polish, and Portuguese), and a second book on Qualitative Research from Start to Finish (2016) is in its 2nd edition and has been translated into four languages (Chinese, Korean, Swedish, and Portuguese).  Dr. Yin received his B.A. in history from Harvard College (magna cum laude) and his Ph.D. in brain and cognitive sciences from MIT.

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• Publisher ‏ : ‎ SAGE Publications, Inc; 3rd edition (December 24, 2002)
• Language ‏ : ‎ English
• Paperback ‏ : ‎ 200 pages
• ISBN-10 ‏ : ‎ 0761925538
• ISBN-13 ‏ : ‎ 978-0761925538
• Item Weight ‏ : ‎ 3.84 ounces
• Dimensions ‏ : ‎ 5.5 x 0.5 x 8.5 inches
• #706 in Social Sciences Research
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About the author

Robert k. yin.

Robert K. Yin, Ph.D., serves as Chairman of the Board and CEO of COSMOS Corporation, an applied research and social science firm that has been in operation since 1980. Over the years, COSMOS has successfully completed hundreds of projects for government agencies, private foundations, and other entrepreneurial and non-profit organizations. At COSMOS, Dr. Yin actively leads various research projects, including those in which the case study method is used. He has authored numerous books and peer-reviewed articles, including Case Study Research and Applications of Case Study Research. In 1998 he founded the “Robert K. Yin Fund” at M.I.T., which supports seminars on brain sciences, as well as other activities related to the advancement of pre-doctoral students in the Department of Brain and Cognitive Sciences.

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Case study research : design and methods

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• Fifth edition
• Los Angeles : SAGE, [2014]
• xxviii, 282 pages : illustrations ; 24 cm
• Includes bibliographical references (pages 243-257) and indexes.
• Getting started: how to know whether and when to use the case study as a research method -- Designing case studies: identifying your case(s) and establishing the logic on your case study -- Preparing to collect case study evidence: what you need to do before starting to collect case study data -- Collecting case study evidence: the principles you should follow in working with six sources of evidence -- Analyzing case study evidence: how to start your analysis, your analytic choices, and how they work -- Reporting case studies: how and what to compose -- Appendix A: A note on the uses of case study research in psychology -- Appendix B: A note on the uses of case study research in evaluations -- Appendix C: Index of individual case studies (cited in BOXES or from expanded case study materials)
• Case method.
• Social sciences -- Research -- Methodology.
• Social Sciences -- methods. Medical Subject Heading
• Research Design. Medical Subject Heading

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• Process: Research Design

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Research design.

Design are the methods of collecting evidence to address the research questions and theories. For example: observation, surveys, archival research, experiments, among others. A few common methods are described below. For an in-depth examination of research designs, we recommend the following sources.

Recommended sources

• SAGE Research Methods Online Information about writing a research question, conducting a literature review, choosing a research method, collecting data, and writing up the findings. Coverage spans the full range of research methods used in the social and behavioral sciences, plus a wide range of methods used commonly in sciences, health sciences, and humanities.
• Sage Research Methods: Methods Map

Research Methods

Action research.

A term that is used to describe a global family of related approaches that integrate theory and action with the goal of addressing important organizational, community and social issues together with those who experience them. It focuses on the creation of areas for collaborative learning and the design, enactment and evaluation of liberating actions through combining action and reflection, in an ongoing cycle of co-generative knowledge." Action research is cyclical as the researcher explores intervention on a problem and moving through observations and evaluations. Related approaches: collaborative research, mixed methods, participatory action research, ethnography, participant observation.  Coghlan, D., & Brydon-Miller, M. (2014). The SAGE encyclopedia of action research (Vols. 1-2). London, : SAGE Publications Ltd doi: 10.4135/9781446294406

Applied Research

Applied research is inquiry using the application of scientific methodology with the purpose of generating empirical observations to solve critical problems in society. It is widely used in varying contexts, ranging from applied behavior analysis to city planning and public policy and to program evaluation. Applied research can be executed through a diverse range of research strategies that can be solely quantitative, solely qualitative, or a mixed method research design that combines quantitative and qualitative data slices in the same project. What all the multiple facets in applied research projects share is one basic commonality—the practice of conducting research in “nonpure” research conditions because data are needed to help solve a real-life problem.  Salkind, N. J. (2010). Encyclopedia of research design (Vols. 1-0). Thousand Oaks, CA: SAGE Publications, Inc. doi: 10.4135/9781412961288

A method that seeks to illuminate a research problem by collecting and detailing observations of a particular entity. Definitions of case study differs across disciplines. Generally, case studies "focus on the interrelationships that constitute the context of a specific entity (such as an organization, event, phenomenon, or person)" and analyze "the relationship between the contextual factors and the entity being studied." The method is adopted with "the explicit purpose of using those insights (of the interactions between contextual relationships and the entity in question) to generate theory and/or contribute to extant theory.  Mills, A. J., Durepos, G., & Wiebe, E. (2010). Encyclopedia of case study research (Vols. 1-0). Thousand Oaks, CA: SAGE Publications, Inc. doi: 10.4135/9781412957397

Causal Design

Causality studies may be thought of as understanding a phenomenon in terms of conditional statements in the form, “If X, then Y.” This type of research is used to measure what impact a specific change will have on existing norms and assumptions. Most social scientists seek causal explanations that reflect tests of hypotheses. Causal effect (nomothetic perspective) occurs when variation in one phenomenon, an independent variable, leads to or results, on average, in variation in another phenomenon, the dependent variable.  From https://libguides.usc.edu/writingguide/researchdesigns

Cohort Design

A design in which groups of individuals pass through an institution such as a school but experience different events such as whether or not they have been exposed to a particular course. The groups have not been randomly assigned to whether or not they experience the particular event so it is not possible to determine whether any difference between the groups experiencing the event and those not experiencing the event is due to the event itself.  Cramer, D., & Howitt, D. (2004). The SAGE dictionary of statistics (Vols. 1-0). London, : SAGE Publications, Ltd doi: 10.4135/9780857020123

Experimental Design

Experiments are ways of assessing causal relationships by, in its simplest form, randomly allocating 'subjects' to two groups and then comparing one (the 'control group') in which no changes are made, with the other (the 'test group') who are subjected to some manipulation or stimulus." "The primary purpose of experimental designs is to establish “cause and effect” or more technically, to make causal inferences.  Frey, B. (2018). The SAGE encyclopedia of educational research, measurement, and evaluation (Vols. 1-4). Thousand Oaks,, CA: SAGE Publications, Inc. doi: 10.4135/9781506326139

Meta-analysis

A statistical method that integrates the results of several independent studies considered to be “combinable.” It has become one of the major tools to integrate research findings in social and medical sciences in general and in education and psychology in particular." Essential characteristics of meta-analysis include: "it is undeniably quantitative, that is, it uses numbers and statistical methods for organizing and extracting information; it does not prejudge research findings in terms of research quality (i.e., no a priori arbitrary and nonempirical criteria of research quality are imposed to exclude a large number of studies); it seeks general conclusions from many separate investigations that address related or identical hypotheses.  Salkind, N. J. (2010). Encyclopedia of research design (Vols. 1-0). Thousand Oaks, CA: SAGE Publications, Inc. doi: 10.4135/9781412961288

Fieldwork or Field Research

Conducted in a natural setting rather than in a laboratory or at a distance. "Researchers examine how the manipulation of at least one independent variable leads to a change in a dependent variable in the context of the natural environment. When researchers conduct experiments, they study how the manipulation of independent variables, or variables that remain constant, cause a change in a dependent variable, or a factor that changes.  Allen, M. (2017). The sage encyclopedia of communication research methods (Vols. 1-4). Thousand Oaks, CA: SAGE Publications, Inc doi: 10.4135/9781483381411

Longitudinal Research

Although the term is used somewhat differently in different disciplines, it generally refers to research involving data collected at more than one point in time and focused on the measurement and analysis of change over time in the units of study.  Sage Research Methods

Ethnography

Ethnography involves the production of highly detailed accounts of how people in a social setting lead their lives, based on systematic and long-term observation of, and discussion with, those within the setting.  Sage Research Methods

Mixed Methods Research

A process of research in which researchers integrate quantitative and qualitative methods of data collection and analysis to best understand a research purpose. The way this process unfolds in a given study is shaped by mixed methods research content considerations and researchers’ personal, interpersonal, and social contexts  Plano Clark, V. & Ivankova, N. (2016). Why a guide to the field of mixed methods research?: introducing a conceptual framework of the field. In Plano Clark, V., & Ivankova, N. Mixed methods research: A guide to the field (pp. 3-30). Thousand Oaks, CA: SAGE Publications, Inc. doi: 10.4135/9781483398341

Clinical Research

Medical research involving people. The aim of clinical research is to advance medical knowledge by collecting evidence to establish treatments, either through observational studies or through experimental research such as clinical trials." Includes: protocols, clinical trials, pre-post studies.  Sage Research Methods

Qualitative Research

Also known as qualitative inquiry, is an umbrella term used to cover a wide variety of research methods and methodologies that provide holistic, in-depth accounts and attempt to reflect the complicated, contextual, interactive, and interpretive nature of our social world. For example, grounded theory, ethnography, phenomenology, ethnomethodology, narratology, photovoice, and participatory action research (PAR) may all be included under the qualitative label, although each of these individual methods is based on its own set of assumptions and procedures.  Salkind, N. J. (2010). Encyclopedia of research design (Vols. 1-0). Thousand Oaks, CA: SAGE Publications, Inc. doi: 10.4135/9781412961288

Quantitative Research

Quantitative research studies produce results that can be used to describe or note numerical changes in measurable characteristics of a population of interest; generalize to other, similar situations; provide explanations of predictions; and explain causal relationships. The fundamental philosophy underlying quantitative research is known as positivism, which is based on the scientific method of research.  Salkind, N. J. (2010). Encyclopedia of research design (Vols. 1-0). Thousand Oaks, CA: SAGE Publications, Inc. doi: 10.4135/9781412961288

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Case Study Research and Applications Design and Methods

• Robert K. Yin - COSMOS Corporation
• Description

Supplements

Password-protected Instructor Resources include the following:

• An expanded glossary provided by the author in the form of downloadable Briefs.
• Additional tutorials written by the author which correspond to Chapters 1, 2, 3, 5, and 6.
• A selection of author Robert Yin's SAGE journal articles.
• Tables and figures from the book available for download.

“The book is filled with tips to the researcher on how to master the craft of doing research overall and specifically how to account for multi-layered cases.”

“Yin covers all of the basic and advanced knowledge for conducting case study and why they are useful for specific research studies without getting lost in the weeds.”

“The applications enhance the original material because it gives the reader concrete examples.”

“Yin is much more in-depth on case study methods both within a general qualitative text and any other case study text I have seen.”

On demand used as recommendation for basic literature for case study research

An essential reading for people doing case studies.

very thoruogh introduction

Very good introduction to Case Study design. I have used case study approach for my PhD study. I would recommend this book for an indepth understanding of case study design for research projects.

Dr Siew Lee School of Nursing, Midwifery and Paramedic Practice Robert Gordon University, Aberdeen.

The book is a really good introduction to case study research and is full of useful examples. I will recommend as the definitive source for students interested in pursuing this further in their projects.

In our Doctor of Ministerial Leadership (DML), Case Study is the Methodology that is required in this program. Robert Yin's book provides the foundational knowledge needed to conduct research using his Case Study design.

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Preface: Spotlighting "Case Study Research"

Chapter 1: Getting Started

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Peer-reviewed

Research Article

The effects of person-centred active rehabilitation on symptoms of suspected Chronic Traumatic Encephalopathy: A mixed-methods single case design

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review & editing

Affiliation Department of Health Professions, Faculty of Health and Education, Manchester Metropolitan University, Manchester, United Kingdom

Roles Conceptualization, Formal analysis, Methodology, Supervision, Writing – review & editing

Roles Conceptualization, Formal analysis, Methodology, Supervision

Affiliation Department of Psychology, Faculty of Health and Education, Manchester Metropolitan University, Manchester, United Kingdom

Roles Conceptualization, Formal analysis, Methodology, Supervision, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

• Rachael Hearn, 
• James Selfe, 
• Maria I. Cordero, 
• Nick Dobbin

• Published: May 30, 2024
• https://doi.org/10.1371/journal.pone.0302260
• Reader Comments

The objective was to investigate the effectiveness of a person-centred active rehabilitation programme on symptoms associated with suspected Chronic Traumatic Encephalopathy (CTE). This was accomplished by (1) assessing the effect that a person-centred active rehabilitation programme had on participant symptoms, and (2) exploring how temporal contextual factors affected the participants’ experience with, and perceived effectiveness of, the active rehabilitation programme.

A twelve-month mixed-methods single case experimental research design was used with six cases (participants). Individual cases were involved in a 51-week study period including an initial interview and three-week baseline phase. Cases were then randomly allocated to one of two n-of-1 study designs (i.e., A-B, B-A, B-A, A-B or B-A, A-B, A-B, B-A) where A and B represent a non-intervention and intervention phase, respectively. Interviews were conducted regularly throughout the study whilst outcome measures were assessed at each follow-up. Analysis of the data included visual, statistical, and qualitative analysis.

Visual and statistical analysis of cognitive and executive function, and mindful attention, demonstrated trivial-to-large effects with the summary reflecting positive or unclear results. A mixed picture was observed for mood and behaviour with effects considered trivial-to-large, and the summary demonstrating positive, unclear and negative effects. Qualitative analysis indicated a perceived improvement in outcome measures such as memory, attention, anxiety, and emotional control despite mixed quantitative findings whilst a clear impact of contextual factors, such as COVID-19, the political atmosphere, exercise tolerance, programme progression, and motivation were evident during the intervention.

Conclusions

This study has provided primary-level evidence to suggest active rehabilitation as a potential intervention for the management of suspected CTE symptoms. This study has also demonstrated the benefit of a person-centred approach to both clinical research and practice, particularly by considering contextual factors for a better understanding of an intervention effect.

Citation: Hearn R, Selfe J, Cordero MI, Dobbin N (2024) The effects of person-centred active rehabilitation on symptoms of suspected Chronic Traumatic Encephalopathy: A mixed-methods single case design. PLoS ONE 19(5): e0302260. https://doi.org/10.1371/journal.pone.0302260

Editor: Simone Varrasi, University of Catania, ITALY

Received: December 21, 2023; Accepted: March 31, 2024; Published: May 30, 2024

Copyright: © 2024 Hearn et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: The data underlying the results presented in this study are available from Manchester Metropolitan University e-space: https://e-space.mmu.ac.uk/view/datasets/ .

Funding: The author(s) received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Chronic Traumatic Encephalopathy (CTE) was formally defined by the National Institute of Neurological Disorders and Stroke/National Institute of Biomedical Imaging and Bioengineering (NINDS/NIBIB) consensus panel in 2015. CTE is a neurodegenerative pathology defined by its unique, irregular pattern of tau protein accumulation around small blood vessels at the base of the cortical sulci [ 1 ]. While CTE has been known by many since at least 1928, the clinical profile has consistently been linked to an exposure to repetitive brain injury. CTE has now been diagnosed post-mortem in former American football, football (soccer), rugby, Australian rules football, ice hockey, baseball, and wrestling athletes, as well as military personnel and domestic abuse victims [ 1 – 3 ]. The inability to diagnose CTE pre-death has led to the development of a clinical profile termed Traumatic Encephalopathy Syndrome (TES). This clinical profile has enabled researchers to identify individuals with symptoms associated with suspected CTE allowing for early management and development of active rehabilitation or treatment options [ 2 , 4 – 6 ].

Currently, no evidence-based therapy has been developed to treat or manage symptoms associated with CTE to our knowledge. Cantu and Budson [ 4 ] provided the first expert review outlining potential lifestyle modifications and symptom management strategies for CTE. Recommendations included exercise, active rehabilitation, diet, cognitive rehabilitation, mood/behavioural therapy, occupational therapy, vestibular and motor therapy, and pharmacological therapy. This expert opinion has been reiterated by Fusco et al. [ 7 ] and Rossi et al. [ 8 ] in expert opinions or narrative reviews. Themes including cognitive and motor rehabilitation therapy, mindfulness, mood/behavioural therapy, occupational therapy, diet, exercise, and active rehabilitation were suggested to help manage neuropsychiatric symptoms of CTE [ 7 , 8 ]. Finally, an umbrella review [ 9 ] has reported the effect that active rehabilitation has on other tauopathies with symptoms associated with CTE. This review found that various forms of active rehabilitation had a positive effect (standardised mean difference ranging from 0.11 to 0.88) on symptoms of cognitive and motor function in populations diagnosed with Alzheimer’s and Parkinson’s disease.

Despite being an area of growing interest amongst researchers and clinicians, current evidence is largely limited to secondary level research. Whilst various forms of management strategies have been suggested (e.g., active rehabilitation), few have examined the efficacy of this. It is also important to consider the patient within a rehabilitation or management approach. A person-centred care approach allows for the management of patients with a unique set of symptoms which is likely to be particularly important when managing individuals with suspected CTE. Accordingly, the objective of this study was to investigate the effectiveness of person-centred active rehabilitation on symptoms of TES, providing the first primary level research exploring a potential management for CTE symptoms. This was accomplished by: (1) assessing the effect that a person-centred active rehabilitation programme had on participant symptoms suspected to be associated with the development of CTE, and (2) exploring how proximal (individual—interpersonal and intrapersonal) and distal (environmental—socio-economic, rural-urban differences and immigration background) factors affected the participants’ experience with, and perceived effectiveness of, the active rehabilitation programme through repeated interviews during the course of the intervention.

Materials and methods

A mixed-methods single case research (MMSCR) design was used for this study with an n-of-1 framework. The study was designed and reported in line with the Consolidated Standards of Reporting Trials (CONSORT) extension for N-of-1 trials [ 10 , 11 ]. Ethical approval was granted by the Faculty of Health, Psychology and Social Care Research Ethics and Governance Committee at Manchester Metropolitan University (ID: 11822).

Eligibility criteria

Individuals between the age 20 and 60 years who met the 2014 TES criteria [ 6 ], spoke/read English, and were at least one year retired from competitive sport were eligible for inclusion. The 2014 TES criteria was used as the updated criteria by Katz and colleagues [ 5 ] was not available at the start of the study. An age range of 20 to 60 years allowed for sufficient exposure to mTBI/contact sport while minimising the chance of concomitant neurodegenerative disease, presence of dementia, and other neurological disorders. Individuals diagnosed with dementia were excluded.

At any time during data collection, withdrawal could be explicitly expressed by the participant. Withdrawal was assumed if the participant (1) missed more than two follow-up interviews in a row, or (2) did not respond to at least two contact attempts made by the researcher seeking to schedule a follow-up interview. Withdrawal was also discussed if the participant expressed dissent with the study procedures. In the event of participant withdrawal, any data where a full data collection cycle had been completed (A-B matched pair) was included in the analysis.

Materials and procedures

General procedure..

Individual cases (participants) were involved for 51 weeks, with recruitment and study commencement occurring on a rolling basis starting in April 2020 and ending in June 2021. The study began with an initial interview, followed by a three-week baseline phase. Participants were then randomly allocated to one of two systematic counterbalanced n-of-1 study designs, the first being A-B, B-A, B-A, A-B and the second being B-A, A-B, A-B, B-A, where ‘A’ indicates a non-intervention phase and ‘B’ indicates an intervention phase. Each paired phase (A-B or B-A) lasted twelve weeks and consisted of six interviews which took place every two weeks. A schematic overview of the study is illustrated in Fig 1 .

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Note: A = non-intervention phase. B–intervention phase.

https://doi.org/10.1371/journal.pone.0302260.g001

Initial interview and screening assessments.

An initial interview was conducted to (1), screen the participant for study eligibility, ensuring they met clinical criteria for the presence of TES, and (2), to screen the participant for evidence of potential cognitive impairment, changes in mood/behaviour, or motor impairment associated with CTE which could be assessed during the three-week baseline period. To date, there is no established battery of assessments relevant to the population used in this study; thus, a pragmatic approach was adopted. The initial interview began with three core screening assessments to measure levels of cognitive function, mood/behavioural symptoms, and motor function ( S1 Table ). The initial meeting concluded with a semi-structured interview that sought to elicit further information related to the eligibility criteria and provided the participant with an opportunity to share information on relevant sporting history, medical history, family medical history, and any other further symptoms or concerns. In line with a person-centred care approach, participants also gave information regarding activity capabilities and preferences to inform the design of the active rehabilitation programme.

Baseline phase and follow-ups.

The three-week baseline period sought to establish the presence of measurable impairment. The assessments used were individualised for each case based on relevance and symptoms reported in the initial interview. Any symptom of TES had the potential for inclusion. A description of all assessments used in the study can be found in S2 Table . To reduce the burden on participants, a five-assessment limit was implemented. For those who did not reach the five-assessment limit, the Perceived Stress Scale (PSS) was included to provide further support to the contextual information gathered during the follow-up interviews.

During each follow-up, participants completed an online survey consisting of self-report symptom assessments. The online survey also gave open box to submit a daily activity log. This log allowed participants to report daily log of their physical activity as well as additional contextual information related to their symptoms and programme experience. Participants also took part in a semi-structured follow-up interview at each data collection point. The semi-structured interviews primarily sought to create a person-centred care environment, promoting factors such as understanding the participant as a person and encouraging involvement in the co-design of the active rehabilitation. The aim of these interviews was to understand i) how the presence of the person-centred active rehabilitation programme affected the symptoms of interest, ii) how the participant described their experience with the rehabilitation programme and prescription, iii) how proximal and distal factors may have influenced the participants symptom levels, and iv) how proximal and distal factors may have influenced their experience with or effect of the programme.

Intervention delivery.

The setting of the study was entirely online. Any outcome assessments used were recorded via Qualtrics XM (Qualtrics, Provo, Utah, USA). The intervention programme was distributed via email and accompanied with online tutorial videos.

During an intervention phase (B phase), participants completed one resistance training session and one cardiovascular session each week. During a non-intervention phase (A phase) the prescribed exercises were removed, but participants were allowed to continue with habitual activities. Care was taken to ensure programme prescriptions resulted in a greater training load during intervention phases relative to the non-intervention phases.

The training programme was tailored by mode, duration, and intensity based on participant needs, preferences, facilities, and strength/fitness levels as understood from the semi-structured interview. Intensity for the resistance training programmes was prescribed using a modified rating of perceived exertion (RPE) scale [ 12 ]. The intensity of the cardiovascular training programme was prescribed using the Borg 6–20 scale given its linear relationship with heart rate [ 12 ].

Data analysis

Quantitative analysis..

Visual analysis of the quantitative data followed a modified framework presented by Wolfe and colleagues [ 13 ], created in accordance with The What Works Clearinghouse (WWC) Single-Case Design Standards [ 14 ]. Initially, a trend in the data was established for each of the paired non-intervention and intervention phases using a split middle trend (SMT) line [ 15 ]. The SMT line was then used to predict outcome measures for the subsequent phase. The size of the effect was estimated using a modified point system [ 13 ] based on the following:

• Evidence of change in level, trend and/or variability = 1.0 point
• Change was immediate, there was less than 30% of data overlap, or there was evidence of consistency between phase-types (intervention/non-intervention) = 0.25 point

After summing the scores, 0–2 indicates unclear behavioural change; 3–4 a small behavioural change; 5–6 a moderate behavioural change; 7–8 a large behavioural change.

To support the visual analysis and future research (e.g., sample size, meta-analyses), within-case standardized mean difference (WC-SMD) and non-overlap of all pairs (NAP) with 95% confidence limits were calculated [ 16 ]. SMDs were classified as: <2.0 trivial; 0.20–0.50, small; 0.51–0.80, moderate; >0.80, large [ 17 ]. NAP was interpreted as a probability that a randomly selected datapoint in the intervention (B) phase was above or below (depending on if an increase or decrease is desirable) a randomly selected datapoint in the non-intervention (A) phase [ 16 ].

Qualitative analysis.

All interviews were transcribed verbatim . Transcriptions were then read to identify content related to the topics of interest based on deductive analysis a-priori . Additional points of interest that also emerged were included via inductive analysis. To maintain trustworthiness through confirmability, all authors were given a random selection of transcripts to analyse. Qualitative analysis followed the explanation building approach outlined by Yin [ 18 ]. The following propositions were initially determined:

• The presence of the person-centred active rehabilitation programme had a positive effect on the participant’s symptoms of interest.
• The needs and preferences of the participant regarding the rehabilitation mode and prescription were met.
• Proximal and distal factors influenced i) the participant’s reported symptom levels, ii) the participant’s experience with the active rehabilitation programme, and iii) the effect of the active rehabilitation programme.

While a total of twenty-four follow-up interviews were available, a pragmatic approach for qualitative analysis was adopted. The sample of interviews used in this study consisted of those that took place at the end of each A-B paired phase (e.g., A1.3, B2.3, B3.3, and A4.3) to provide a more global view of the participant perspective as it related to the phase (whether A or B) and proximal and distal factors. A summary of results is presented in a narrative and visual format.

Participant characteristics

Ten participants were recruited for the study. Two participants did not demonstrate a measurable impairment during the screening or baseline phase in one of the three core clinical features and therefore did not meet eligibility criteria. A further two participants withdrew from the study before they completed an entire A-B phase. In both instances, the participant did not respond to at least two contact attempts made by the primary author to schedule follow-up interviews. A reason for withdrawal was not stated by either participant. In line with the study protocol, their data was withdrawn from the study. A total of six participants completed all aspects and were included in the final analysis.

Participant characteristics, informed by the initial semi-structured interview and baseline phase, can be found in Table 1 . Results are presented using pseudonyms to maintain anonymity.

https://doi.org/10.1371/journal.pone.0302260.t001

Fig 2 illustrates a complete study timeline across all participants along with the sequence of intervention (B) and non-intervention (A) phases. This figure also provides key information on the COVID pandemic and the restrictions in place for each participant at the time of data collection.

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Fig 3 presents results from the PSS assessment.

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Participant activity levels

Participant were habitually active during the intervention engaging in various forms of physical activity including leisure, exercise, and sport. Table 2 presents a summary of the activities reported by participants during both intervention (B) and non-intervention (A) phases with bolded text being the prescribed activities.

https://doi.org/10.1371/journal.pone.0302260.t002

Quantitative analysis

Table 3 provides a summary of the six individual cases, including visual and statistical analysis, across each symptom of interest. Individual case results can be found in S3 – S8 Tables. The effect that active rehabilitation had on symptoms of motor function was not reported as no participants included in the study had any measurable motor impairments.

https://doi.org/10.1371/journal.pone.0302260.t003

Figs 4 and 5 provide visual results of outcome measures related to cognitive function. Effects on general cognitive function ( Fig 4 ) varied, with one participant (Niall) demonstrating a positive effect, one participant (Kristen) demonstrating a negative effect, and one participant (Simon) demonstrating an unclear effect. It should be noted that levels of general cognitive function consistently demonstrated an upward trend across intervention phases throughout the study for Simon, indicating a potential positive effect; however, statistical analysis supports an unclear effect. Visual and statistical analysis observed consistent overlap in all three cases as well. Levels of cognitive function were higher in the final phase for all three cases compared to those levels reported in the first study phase. Effects on mindful attention ( Fig 4 ) also varied, with one case demonstrating negative visual and statistical analysis (Simon) and one demonstrating a small visual but trivial statistical effect (Abel). High levels of variability throughout the study should be noted here along with consistent overlap between phases; therefore, it is difficult to determine the effect active rehabilitation had on levels of mindful attention.

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Though the WC-SMD ranged from trivial to large, four of the six participants demonstrated a positive effect (Niall, Luigi, Abel, Simon) for measures of executive function ( Fig 5 ). Three of these participants (Niall, Luigi, Simon) also reported higher levels of executive function at the final phase of the study compared to the start of the study. Only Abel reported worse scores during the final phase of the study; however, a large WC-SMD (1.69) and NAP value of 0.79 suggests a positive effect of active rehabilitation overall. It should be noted that Kristen consistently demonstrated decreased variability of scores in non-intervention phases indicating more stable results for executive function in the absence of an active rehabilitation programme. This would suggest that the presence of an active rehabilitation programme had the potential to influence levels of outcome measures, albeit with a lack of statistical certainty. All cases demonstrated consistent overlap with visual analysis; however, NAP values in three cases (Niall, Abel, Simon) demonstrated a higher probability of increased executive function in intervention phases.

Figs 6 and 7 provide visual results of outcome measures related to mood and behaviour. The effect of active rehabilitation on outcome measures considered ‘core clinical features’ according to TES clinical criteria (depression, irritability, social isolation/loneliness) ( Fig 6 ) varied. One participant (Luigi) demonstrated a large positive effect on levels of depression, supported by both visual and statistical analysis; however, three participants (Kristen, Abel, Simon) demonstrated a small, negative effect on levels of depression. Interestingly, all participants aside from one (Simon) reported lower levels of depression during the final phase of the study compared to initial levels. There was no consistency of patterns in variability or trend, but overlap between phases was consistently present. NAP values also varied, indicating a variation in the likelihood of a randomly selected point taken during an intervention phase resulting in lower depression scores. Only one participant reported symptoms of loneliness and social isolation (Niall), and one participant reported symptoms of irritability (Luigi). In both instances, visual analysis indicated a positive effect. Levels of loneliness demonstrated a consistent downward trend during intervention phases despite increased variability. It should also be noted that Luigi demonstrated decreased variability for levels of irritability across intervention phases. A positive effect is further supported by improved levels reported during the final phase of the study compared to initial levels, as well as a general decline observed across the entire study; however, statistical analysis reports a trivial effect in both outcome measures.

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https://doi.org/10.1371/journal.pone.0302260.g007

The effect of active rehabilitation on outcome measures considered ‘supportive clinical features’ according to TES clinical criteria (anxiety, sleep quality/insomnia) ( Fig 7 ) also varied. One participant (Luigi) reported a small-to-moderate effect on levels of anxiety, supported by visual and statistical analysis; however, Kristen and Abel reported a moderate, negative effect. The effect of active rehabilitation on Gemma’s level of anxiety was unclear. Visual analysis demonstrated a small effect; however, statistical analysis reports the effect as trivial. Interestingly, all participants demonstrated reduced levels of anxiety during the final phase of the study compared to those levels reported during the initial phase; however, overlap was present between all phases across all cases suggesting a temporal pattern of change. Only Kristen reported NAP levels which could suggest a greater probability of lower levels of anxiety in non-intervention phases (NAP = 0.25). It should be noted that Gemma consistently demonstrated a downward trend in levels of anxiety in intervention phases. Only one participant reported symptoms of reduced sleep quality and insomnia (Kristen). Despite WC-SMD reporting a small negative effect, visual analysis reported a trivial effect. Further, NAP suggests the probability randomly selected data point for sleep score being lower during an intervention phase was 43%. It should be noted that Kristen’s sleep score was lower at the end of the study compared to those reported at the start of the study, indicating an improvement in symptoms.

Qualitative data

Fig 8 presents a visual summary of the topics emerged from the semi-structured interviews, including information relevant to the context of the study (8A), intervention experience (8B), and perception towards the effect of the intervention on symptoms (8C). Topics of discussion highlighted in green present information that may have contributed to a positive participant experience and generally included improved memory, coping skills emotional control and anxiety, the role of goal setting, and satisfaction with the active rehabilitation programme. Topics of discussion highlighted in red present a potentially negative experience. These include information such as COVID-19 and the political atmosphere as well as exercise tolerance, progression, and motivation. Topics of discussion highlighted in yellow presented points that were not clearly linked to a positive or negative experience (e.g., weather, unclear or neutral feelings, and preferences).

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The most obvious influence that emerged from the results which impacted every participant was the presence of the COVID-19 pandemic and subsequent lockdown restrictions. This seemed to influence Niall and Luigi the most. These two participants began the study at the very start of the pandemic where restrictions were the harshest and the levels of uncertainty were the highest. It seemed to affect Kristen the least, who lives in a quite secluded part of New York (state). The presence of the pandemic had both a direct and indirect effect on the success of the intervention. The pandemic influenced some outcomes of interest such as symptoms of anxiety and depression. Lockdown restrictions could also influence executive function as illustrated by Niall, who reported that motivation, attention, and concentration were disrupted. It should be noted that two participants contracted COVID-19 during the study (Kristen, Abel), resulting in further direct effects of the global pandemic. Indirectly, COVID-19 and subsequent lockdowns also impacted socialisation which had a notable impact on Niall, Abel, and Gemma. That said, we do also acknowledge that the pandemic and ‘stay at home’ messaging did facilitate a home-based active rehabilitation programme whereby greater leisure time was available for some due to reduced travel to and from working and social commitments.

The political discourse present in the United States affected the three American participants to varying degrees. Abel considers himself passionate about, and therefore hyper-involved in, the political culture of the US. Therefore, the BLM protests, the Capitol attack, and the Presidential election resulted in increased feelings of stress. This effect was vastly reduced in the second half of the study following the end of the election cycle, as evidenced in the PSS scores. While still affected by the same factors, Gemma was less involved and therefore found that the political discourse had more of an ‘exhausting’ effect and produced feelings of irritability. Finally, Kristen reported some levels of stress concerning the present circumstances; however, she was better able to cope as she was not as directly exposed to some of the unrest living in a secluded area compared to Abel and Gemma who were more city-based.

Work was another factor that was mentioned by several participants. As someone working in the healthcare industry, who also received a work promotion during the study, Luigi felt direct pressure from the COVID-19 pandemic. This was evidenced in his PSS scores. Abel and Gemma both suffered from job instability. Abel changed jobs at least three times during the study, as each position was more seasonal in nature and induced a degree of anxiety and frustration as well as resulting in periods of physically demanding work. Gemma’s work was directly impacted by the COVID-19 pandemic. After the onset of the pandemic, her job position became less stable. She tried taking on per diem work, but regardless her work situation was unstable largely throughout the study. In contrast, Simon reported a positive effect on his general well-being after returning to work following a prolonged period of medical leave.

Programme prescription and activity selection was another factor that emerged from the data. Exercise intolerance was present in two participants (Kristen, Simon) who both reported a history of moderate-to-severe TBI. Kristen struggled with fully participating in the study as a direct result of her exercise intolerance. While she was willing to ‘push through’ some short-term adverse reactions, she expressed that any time she overcame her exercise intolerance, the phase would change to a non-intervention phase and she had to start all over again during the next intervention phase. This sentiment is further supported by reported outcome measures in phase B4, which occurred immediately after phase B3 resulting in a double intervention phase. When given an additional six weeks of intervention, levels were improved for cognitive function, anxiety, and depression. Simon’s exercise intolerance was less severe, but it did have an impact on what activities could be prescribed. He did not report any adverse events because of the programme, aside from his difficulty with constant disruption and lack of control over his programmes. COVID-19 and subsequent lockdowns resulted in the disruption of preferred activities for several participants. Niall was not able to go to the gym or consistently take part in field hockey which he reported was a source of frustration. Not only were these his preferred activities, but both involved an element of socialisation and associated social capital. Luigi noted that he struggled to find ‘me time’ as he never felt comfortable returning to the gym even when it was open despite this being his preferred setting due to a fear of contracting COVID-19. Simon struggled with the inconsistency of gym availability which resulted in constant changes to his programmes. Finally, the weather had both a positive and a negative impact on activity selection depending on the time of year. Niall, Luigi, Abel, and Gemma all preferred outdoor activities, which meant participants enjoyed activity more in the warmer and less rainy months of the year when they could get outside. Despite these factors, various participants still expressed satisfaction with their programmes (Niall, Luigi, Gemma). Positive experiences were increased when the intervention utilised a goal-setting element to increase motivation (Niall, Luigi, Simon).

This mixed-methods single case design provides the first primary level evidence to suggest that active rehabilitation has potential as an intervention for those suffering from symptoms related to suspected CTE. Overall, active rehabilitation had a largely positive effect on measures of cognitive function whilst the results for mood and behaviour across the intervention period was mixed and heavily influenced by factors such as the COVID-19 pandemic.

Quantitative analysis suggests that active rehabilitation had an almost equally positive and unclear effect on overall cognitive function. These findings reflect that reported by Hearn et al. [ 9 ] who observed a pooled estimate across three studies as moderately positive but with confidence intervals crossing positive, unclear, and negative effects on cognitive function in populations with tau pathologies. Considering the outcome measures of general cognitive function (one positive, one trivial, one negative), the effect of active rehabilitation was inconclusive and suggestive of individual variation. The effect of active rehabilitation on measures of general cognitive function were inconclusive, with one trivial effect and one negative effect reported. Across the study, the only impairment observed in all participants was executive dysfunction. This supports the inclusion of memory impairment and executive dysfunction in the updated TES criterion presented by Katz and colleagues [ 5 ]. Four of the six participants reported a positive effect for executive function overall (Niall, Luigi, Abel, Simon) with two others being unclear (Kristen, Gemma). Importantly, there was no negative effect observed on measures of executive function. Overall, the effect of active rehabilitation on cognitive function has yet to be fully determined but is promising. While the underlying physiological mechanisms are yet to be fully understood, exercise is known to have a positive impact on neurogenesis and angiogenesis [ 19 , 20 ] which can have a positive influence on executive function.

The results for mood and behaviour symptoms were largely inconclusive. When considering the individual outcome measures, one positive, one trivial, and two negative effect were observed for anxiety. Whilst this outcome is surprising from a purely quantitative viewpoint, based on the qualitative results, it is unlikely that these effects are attributed solely to the active rehabilitation programme. For example, the qualitative data suggests COVID-19 and subsequent lockdowns had both a direct and indirect effect on many of these outcomes. Participants expressed how the consequences of lockdowns in response to the pandemic directly influenced symptom levels. Specifically, lockdowns negatively influenced components of executive function, as well as levels of anxiety and depression. One participant (Gemma) further expressed her feelings of fear and anxiety about the presence of the virus itself, specifically about the danger it posed to her loved ones. These findings reflect similar observations in various populations where the COVID-19 pandemic resulted in higher reported levels of stress, anxiety, and depression [ 21 , 22 ]. Supported by the PSS scores and participant interviews, the influence was likely stronger earlier on in the intervention period as participants eventually began to adapt to life with COVID-19. For those who contracted the virus (Kristen, Abel), symptom levels were also likely influenced by the presence of the virus. In addition to the respiratory and inflammatory symptoms associated with COVID-19, contracting COVID-19 has also been associated with the development of fatigue, anxiety, depression, and cognitive disturbances [ 23 ].

Despite the various proximal and distal factors being discussed, some of which were unprecedented and, at times, had a substantial influence on participant symptoms, this study was still able to provide positive results. Supported by the quantitative results, participants directly reported that they felt the active rehabilitation programme had a positive effect on symptoms of memory, attention, depression, and anxiety. It was suggested the effect may have been cumulative across the twelve-month intervention period (Kristen, Abel, Gemma). This is supported by the improvement of various outcome measures at the end of the study despite conflicting visual and/or statistical analysis, such as the improvement in levels of cognitive function in the case of Kristen or the improvement in levels of depression in the case of Abel. At the very least the programme offered a way to cope with or better manage symptoms as suggested by Luigi, Abel, Gemma. This is demonstrated by the consistent decreased variability in levels of irritability (Luigi) and loneliness (Niall) consistently observed during intervention phases despite a reported trivial effect. If repeated under more stable conditions, there is a potential for a greater, and perhaps stronger, number of observed positive effects, especially when considering the greater understanding of the context and individual preferences that emerged in this study. Further, some of the participants may not have met the eligibility criteria had these unprecedented factors not been present. For example, Niall’s levels of loneliness were only above reported population average during the baseline phase and proceeded to drop throughout the first half of the study independent of the active rehabilitation programme. Therefore, future research and clinical practice might consider symptoms and inclusion criteria that are evident outside of other factors such as the environment and personal circumstances.

This study also supports the use of a person-centred approach in future research and clinical care, as evidenced by the enhanced understanding of participant context and study experience. Utilising a mixed methods approach with data integration has allowed for an in-depth understanding of the observed visual and statistical results. This was further enhanced by the study length (twelve months). A person-centred approach to programme prescription ensured participant satisfaction and reduced dropouts. This is evidenced by the six participants who completed the twelve-month study and reported programme satisfaction despite many not having access to preferred activities.

Whilst this study is the first empirical investigation within this area, this study is not without some limitations. Firstly, we note that some features of the study might limit the generalisability of the findings. Indeed, the TES criteria was updated after the study commenced, the study was carried out during a pandemic, and the outcomes lack specificity to a a suspected CTE population. Secondly, whilst online methods were essential for the success of this study, there is an inherent lack of control over aspects such as other activities and the intensity these are performed which would impact some outcomes used in the study. Also, the online nature meant that outcomes were limited to questionnaires and qualitative data whereas objective measure to supplement these might have strengthened the validity of these findings. Future research should continue to utilise a person-centred approach within this area of enquiry to improved intervention efficacy while continuing to maintain study adherence and participant satisfaction. Also, future work should seek substantiate the findings in this study to allow for pooling of data.

In conclusion, this study has provided evidence to establish the potential use of active rehabilitation for the management of suspected CTE using a mixed-methods single case research design. Based on the results of this study, a narrative summary of the integrated qualitative and quantitative results has been provided in Table 4 . This table provides a holistic understanding of individual cases and observed effects supporting an overall conclusion, though we do refer readers to the individual cases in S3 – S8 Tables given the person-centred approach of the study. This study has offered preliminary evidence which suggests active rehabilitation may offer some benefit to individuals with symptoms of suspected CTE and warrants further investigation using standardised and innovative methodologies. This study has also demonstrated the benefit of a person-centred approach to both clinical research and practice. Considering factors such as personal circumstances, cultural climate, and a detailed intervention response allows for a better understanding of an intervention effect within the context of the study.

https://doi.org/10.1371/journal.pone.0302260.t004

Supporting information

S1 table. screening assessment..

MCI: mild cognitive impairment; PROMIS: Patient-reported outcomes measurement information system. N/A: not applicable due to multiple subscales used.

https://doi.org/10.1371/journal.pone.0302260.s001

S2 Table. Outcome assessments.

https://doi.org/10.1371/journal.pone.0302260.s002

S3 Table. Niall’s summary of results.

https://doi.org/10.1371/journal.pone.0302260.s003

S4 Table. Luigi’s summary of results.

https://doi.org/10.1371/journal.pone.0302260.s004

S5 Table. Kristen’s summary of results.

https://doi.org/10.1371/journal.pone.0302260.s005

S6 Table. Abel’s summary of results.

https://doi.org/10.1371/journal.pone.0302260.s006

S7 Table. Gemma’s summary of results.

https://doi.org/10.1371/journal.pone.0302260.s007

S8 Table. Simon’s summary of results.

https://doi.org/10.1371/journal.pone.0302260.s008

This paper is in the following e-collection/theme issue:

Published on 27.5.2024 in Vol 8 (2024)

This is a member publication of University of Colorado Denver HARC

Lessons Learned From a Sequential Mixed-Mode Survey Design to Recruit and Collect Data From Case-Control Study Participants: Formative Evaluation

Authors of this article:

Original Paper

• Amanda D Tran 1 , MPH   ; 
• Alice E White 1 , MPH   ; 
• Michelle R Torok 1 , PhD   ; 
• Rachel H Jervis 2 , MPH   ; 
• Bernadette A Albanese 3 , MD, MPH   ; 
• Elaine J Scallan Walter 1 , MA, PhD  

1 Department of Epidemiology, Colorado School of Public Health, University of Colorado, Aurora, CO, United States

2 Colorado Department of Public Health and Environment, Denver, CO, United States

3 Adams County Health Department, Brighton, CO, United States

Corresponding Author:

Elaine J Scallan Walter, MA, PhD

Department of Epidemiology

Colorado School of Public Health

University of Colorado

13001 East 17th Place

3rd Floor, Mail Stop B119

Aurora, CO, 80045

United States

Phone: 1 303 724 5162

Email: [email protected]

Background: Sequential mixed-mode surveys using both web-based surveys and telephone interviews are increasingly being used in observational studies and have been shown to have many benefits; however, the application of this survey design has not been evaluated in the context of epidemiological case-control studies.

Objective: In this paper, we discuss the challenges, benefits, and limitations of using a sequential mixed-mode survey design for a case-control study assessing risk factors during the COVID-19 pandemic.

Methods: Colorado adults testing positive for SARS-CoV-2 were randomly selected and matched to those with a negative SARS-CoV-2 test result from March to April 2021. Participants were first contacted by SMS text message to complete a self-administered web-based survey asking about community exposures and behaviors. Those who did not respond were contacted for a telephone interview. We evaluated the representativeness of survey participants to sample populations and compared sociodemographic characteristics, participant responses, and time and resource requirements by survey mode using descriptive statistics and logistic regression models.

Results: Of enrolled case and control participants, most were interviewed by telephone (308/537, 57.4% and 342/648, 52.8%, respectively), with overall enrollment more than doubling after interviewers called nonresponders. Participants identifying as female or White non-Hispanic, residing in urban areas, and not working outside the home were more likely to complete the web-based survey. Telephone participants were more likely than web-based participants to be aged 18-39 years or 60 years and older and reside in areas with lower levels of education, more linguistic isolation, lower income, and more people of color. While there were statistically significant sociodemographic differences noted between web-based and telephone case and control participants and their respective sample pools, participants were more similar to sample pools when web-based and telephone responses were combined. Web-based participants were less likely to report close contact with an individual with COVID-19 (odds ratio [OR] 0.70, 95% CI 0.53-0.94) but more likely to report community exposures, including visiting a grocery store or retail shop (OR 1.55, 95% CI 1.13-2.12), restaurant or cafe or coffee shop (OR 1.52, 95% CI 1.20-1.92), attending a gathering (OR 1.69, 95% CI 1.34-2.15), or sport or sporting event (OR 1.05, 95% CI 1.05-1.88). The web-based survey required an average of 0.03 (SD 0) person-hours per enrolled participant and US $920 in resources, whereas the telephone interview required an average of 5.11 person-hours per enrolled participant and US $70,000 in interviewer wages.

Conclusions: While we still encountered control recruitment challenges noted in other observational studies, the sequential mixed-mode design was an efficient method for recruiting a more representative group of participants for a case-control study with limited impact on data quality and should be considered during public health emergencies when timely and accurate exposure information is needed to inform control measures.

Introduction

Often used during disease outbreak investigations, case-control studies that retrospectively compare people who have a disease (case participants) with people who do not have the disease (control participants) are an efficient and relatively inexpensive method of identifying potential disease risk factors to guide control measures and interventions. Perhaps the most critical and challenging component of conducting a case-control study is the recruitment of appropriate control participants who are from the same source population as case participants [ 1 ]. Because control participants are not ill and may not be connected to the outbreak, they may be less motivated to complete a lengthy questionnaire that collects personal information and detailed exposure histories [ 2 - 4 ]. Moreover, with the increased use of mobile telephones and the routine use of caller ID, study participants contacted by traditional telephone-based survey methodologies may be less likely to answer the telephone [ 5 , 6 ], further reducing the opportunity for participant screening and recruitment.

Recruitment challenges are not unique to case-control studies, and other types of observational studies have shifted from traditional telephone interviews to web-based surveys with the goal of reaching larger groups of people more efficiently and at a lower cost [ 7 - 12 ]. While offering some advantages over traditional telephone interviews, web-based surveys often experience lower response rates and lower data quality [ 13 ], and some studies have found demographic differences between telephone and web-based survey participants, likely driven in part by disparities in internet connectivity and access [ 14 ]. For this reason, researchers have increasingly used both telephone interviews and web-based surveys in a sequential mixed-mode design, first contacting participants using a self-administered web-based survey, and then following up with nonresponders with an interviewer-administered telephone survey [ 15 ]. In other types of observational studies, this mixed-mode design has been shown to reduce selection bias, reduce costs, improve data quality, and result in higher response rates and faster participant recruitment [ 16 , 17 ], making it an appealing design choice for case-control studies.

In March 2020, the World Health Organization declared COVID-19 a global pandemic, and throughout many countries, public health or other governmental authorities implemented stay-at-home orders, travel restrictions, and other public health interventions to reduce disease transmission. In the absence of adequate data-driven evidence about community risk factors for COVID-19 transmission, we implemented a sequential mixed-mode case-control study design in Colorado to evaluate community exposures and behaviors associated with SARS-CoV-2 infection and inform public health control measures. While the benefits and limitations of sequential mixed-mode designs have been well-documented in other contexts [ 14 , 16 , 18 - 20 ], they have not been examined in the context of rapidly implemented epidemiological case-control studies. In this paper, we discuss the challenges, benefits, and limitations of using a sequential mixed-mode survey design using web-based surveys disseminated via SMS text message and telephone interviews for a case-control study assessing exposures during a public health emergency. Specific aims are (1) to compare the sociodemographic characteristics of web-based and telephone survey participants, (2) to evaluate the representativeness of survey participants to the sample population, (3) to assess the completeness of participant responses by survey mode, and (4) to estimate the time and resources required to recruit web-based and telephone survey participants.

Case-Control Study Design and Implementation

The case-control study was conducted among Colorado adults aged 18 years and older who had a positive (case) or negative (control) SARS-CoV-2 reverse transcription-polymerase chain reaction test result in Colorado’s electronic laboratory reporting (ELR) system with a specimen collection date from March 16 to April 29, 2021 [ 21 ]. Eligible individuals testing positive with a completed routine public health interview in Colorado’s COVID-19 surveillance system were randomly selected and individually matched on age (±10 years), zip code (urban areas) or region (rural and frontier areas), and specimen collection date (±3 days) with up to 20 individuals with a negative test, with the goal of enrolling 2 matched controls per enrolled case.

Self-administered (web-based) and interviewer-administered (telephone) case and control surveys were developed in Research Electronic Data Capture (REDCap; Vanderbilt University). REDCap is a secure, web-based platform designed to support data capture for research studies [ 22 ]. The surveys asked about contact with a person with confirmed or suspected COVID-19, travel history, employment, mask use, and community exposure settings (bar or club; church, religious, or spiritual gathering; gathering; grocery or retail shopping; gym or fitness center; health care setting; restaurant, cafe, or coffee shop; salon, spa, or barber; social event; or sports or sporting events) during the 14 days before illness onset or specimen submission. The full survey questionnaire is available in Multimedia Appendix 1 . Demographic data were obtained from Colorado’s COVID-19 case surveillance system and the control survey. Web-based surveys were offered in English and Spanish and included clarifying language, prompts, skip logic, text piping, and progress bars. Interviewers used computer-assisted telephone interviewing in REDCap with scripting and language line services when needed. Questions and response options were identically worded in the web-based and telephone surveys, with the exception of a “refused” option for questions in the telephone survey.

Using the Twilio integration in REDCap, selected individuals were sent an SMS text message to the telephone number provided at the time of testing (which may include both landlines and mobile phones) 3 to 7 days after their specimen collection date, inviting them to complete the web-based survey. A team of trained interviewers began contacting nonresponders for telephone interviews approximately 3 hours after the initial SMS text message was sent, making 1 contact attempt for individuals testing positive for SARS-CoV-2 and up to 2 contact attempts for those testing negative. Interviewers only contacted as many controls by telephone as needed to enroll 2 matched controls per enrolled case. The web-based survey link was resent via SMS text message or sent via email when requested. When possible, voicemail messages were left encouraging SMS text message recipients to complete the web-based survey. As the goal of the case-control study was to assess the risk of SARS-CoV-2 infection from community exposures, we only included surveys that had responses to all 15 community exposure questions. Partial surveys that did not have complete community exposure data were excluded from analyses. Individuals were also excluded if they reported living in an institution, close contact with a household member with confirmed or suspected COVID-19, receiving ≥1 dose of a COVID-19 vaccine (which was not universally available in Colorado at the time of the study), symptom onset date >7 days from specimen collection (case participants), a prior positive COVID-19 result (control participants), or providing personal identifying information in the web-based survey that was inconsistent with information from the ELR system (control participants).

Evaluation of a Sequential Mixed-Mode Survey Design

We evaluated the impact of conducting the COVID-19 case-control study using a sequential mixed-mode design by (1) comparing the sociodemographic characteristics of web-based and telephone survey participants, (2) evaluating the representativeness of study participants to the sample population, (3) assessing the completeness of participant responses by survey mode, and (4) estimating the time and resources required to recruit web-based and telephone survey participants. All analyses were performed using SAS (version 9.4; SAS Institute).

Comparison of Web-Based and Telephone Survey Participants

Case and control participants were eligible individuals who completed the web-based or telephone survey. We compared the demographic characteristics (age, gender, race and ethnicity, geographic location, working outside the home, and socioeconomic factors) of case and control participants completing the web-based and telephone survey to each other using 2-tailed t tests, Pearson χ 2 , or Fisher exact tests. Socioeconomic factors, which are not routinely asked in surveillance and therefore not included in the survey, were evaluated by aggregating mean scores for 4 Colorado EnviroScreen indicators (less than high school education, linguistic isolation, low income, and people of color) based on the participant’s county of residence. Colorado EnviroScreen (version 1.0; Colorado State University and the Colorado Department of Public Health and Environment) is a publicly available environmental justice mapping tool developed by the Colorado Department of Public Health and Environment and Colorado State University that evaluates 35 distinct environmental, health, economic, and demographic indicators. Colorado EnviroScreen scores range from 0 to 100, with the highest score representing the highest burden of health injustice.

Representativeness of Study Participants

We compared the demographic characteristics (as described earlier) of case and control participants completing the web-based and telephone surveys (separately and combined) to the sample pool of all randomly selected individuals testing positive (case sample pool) or negative (control sample pool) for SARS-CoV-2 using 2-tailed t tests, Pearson χ 2 , or Fisher exact tests.

Participant Responses

We evaluated data completeness and differential responses between web-based and telephone survey modes by comparing responses to exposure and behavior questions we deemed prone to social desirability bias (close contact with individuals with confirmed or suspected COVID-19, community exposures, travel, and mask use). Two bivariate logistic regression models, the first adjusting for case-control status and the second adjusting for case-control status and sociodemographic variables shown to be associated with mode effects (age, gender, race and ethnicity, and geographic location), examined the association between survey mode and participant response. Question nonresponse, where data were missing or refused, was evaluated for these questions as well as for other questions with free-text or multiple-choice response options (industry, occupation, reasons for COVID-19 testing, and mask type).

Time and Resource Needs

The time spent by study personnel contacting potential participants by SMS text message and telephone was obtained from self-recorded data in timesheets and used to calculate the person-hours required per enrolled participant. Total expenditures for the web-based and telephone surveys were calculated using staff wages and Twilio texting costs (an average of US $0.008 for a 160-character SMS text message).

Ethical Considerations

The case-control study was deemed by the Colorado Multiple Institutional Review Board to be public health surveillance and not human participant research and was therefore exempt from full approval and requirements for informed consent (protocol 21-2973).

Case and Control Participant Enrollment

The case sample pool included 1323 individuals. Of these, 318 (24%) responded to the web-based survey, and 331 (25%) were interviewed by telephone ( Figure 1 ). A total of 537 (40.6%) case participants were enrolled after excluding 78 (5.9%) partial and 34 (2.6%) ineligible survey responses. Of the 10,898 individuals in the control sample pool, 1072 (9.8%) responded to the web-based survey, and 1268 (11.6%) were interviewed by telephone. A total of 648 (5.9%) control participants were enrolled after excluding 1565 (14.4%) partial and 127 (1.2%) ineligible surveys. Of the enrolled case and control participants, most were interviewed by telephone (308/537, 57.4% and 342/648, 52.8%, respectively).

Case participants completing the web-based and telephone surveys were similar in age (mean 37, SD 13.21 and 14.69 years, respectively), whereas web-based control participants were slightly older than those completing the telephone survey (mean 38, SD 12.44 vs mean 36, SD 12.62 years, respectively; Table 1 ). For both case and control participants, those aged 40-59 years were more likely to complete the web-based survey, whereas participants aged 18-39 years and 60 years and older were more likely to complete the telephone survey. Web-based case and control participants were more likely to identify as female, White, non-Hispanic, reside in urban areas, and be less likely to work outside the home. Compared to web-based case and control participants, telephone participants had higher EnviroScreen scores for all socioeconomic indicators, indicating they resided in counties with larger populations of individuals with less than high school education, linguistic isolation, low income, and people of color.

a Individuals with a positive SARS-CoV-2 test result.

b Individuals with a negative SARS-CoV-2 test result.

c P <.05; control participant web-based versus telephone.

d P <.01; survey mode (web-based, telephone, and web-based and telephone combined) versus sample pool.

e P <.05; case participant web-based versus telephone.

f P <.05; survey mode (web-based, telephone, and web-based and telephone combined) versus sample pool.

g Information on sex and working outside the home were not available from Colorado’s electronic laboratory reporting system for control participants.

h Not available.

i Colorado EnviroScreen is an environmental justice mapping tool. Scores are assigned at the county level, with a higher score indicating that an area is more likely to be affected by the indicated health injustice.

There were statistically significant sociodemographic differences noted between web-based and telephone case and control participants and their respective sample pools ( Table 1 ). More web-based case participants identified as female (134/228, 58.8%) than those in the case sample pool (642/1318, 48.7%). More web-based control participants identified as White, non-Hispanic (205/267, 76.8%) than those in the control sample pool (4467/7812, 57.2%) and more often resided in urban areas (247/306, 80.7%) than those in the control sample pool (7841/10,898, 71.9%). Case and control participants were more similar to their respective sample pools when evaluated as a single group (total enrolled).

In the model adjusting for case or control status only, web-based participants were less likely to report close contact with an individual with COVID-19 when compared to telephone participants (odds ratio [OR] 0.70, 95% CI 0.53-0.94) but more likely to report community exposures including visiting a grocery store or retail shop (OR 1.55, 95% CI 1.13-2.12), visiting a restaurant or cafe or coffee shop (OR 1.52, 95% CI 1.20-1.92), attending a gathering outside the home (OR 1.69, 95% CI 1.34-2.15), or attending or participating in a sport or sporting event (OR 1.05, 95% CI 1.05-1.88) in 14 days before symptom onset or specimen collection ( Table 2 ). When adjusted for case or control status, age, gender, race and ethnicity, and geographic location, the only associations that remained statistically significant were close contact (adjusted OR 0.65, 95% CI 0.48-0.88) and gatherings (adjusted OR 1.44, 95% CI 1.12-1.85).

a Full survey questions are available in Multimedia Appendix 1 .

b Adjusted for case or control status.

c OR: odds ratio.

d Adjusted for case or control status, age, gender, race and ethnicity, and geographic location.

e N/A: not applicable.

Question nonresponse was low across both modalities, with similar ranges of missingness between the web-based survey (0/535, 0% to 22/535, 4.1%) and telephone survey (2/650, 0.3% to 34/650, 5.2%). Nonresponse to industry, occupation, and masking questions was higher in the telephone survey (9/650, 1.4% to 34/650, 5.2%) than the web-based survey (1/535, 0.2% to 22/535, 4.1%; Table 2 ).

Over the course of the study, staff spent a cumulative 15 hours randomly selecting and texting potential participants for the web-based survey, averaging 0.03 person-hours per enrolled participant (15 person-hours per 535 web-based participants) and US $500 in staff wages. Twilio texting costs were US $420, amounting to US $920 in total expenditures for the web-based survey. Comparatively, 3319 hours were spent by interviewers attempting to contact nonresponders by telephone, for an average of 5.11 person-hours per enrolled participant (3319 person-hours per 650 telephone participants) and US $70,000 in interviewer wages.

Principal Findings

While the web-based survey was more time- and cost-efficient than the telephone interview, participant enrollment was low, and there were statistically significant sociodemographic differences between the web-based case and control participants and their respective sample pools. Adding the follow-up telephone interview increased participant enrollment and the representativeness of both the case and control participants to sample pools. Participant responses to exposure and behavior questions and data completeness were similar between the 2 survey modalities.

Enrollment more than doubled for case and control participants after interviewers called individuals who did not respond to the web-based survey to complete the survey by telephone. Case participant enrollment for our mixed-mode study was higher than those for other COVID-19 case-control studies using telephone only (40.6% vs 3%-25% case participant enrollment in other studies), but control participant enrollment was lower (5.9% vs 9%-13% control participant enrollment in other studies) [ 23 - 25 ]. However, control participant enrollment in our sequential mixed-mode study may not be comparable to telephone-only COVID-19 case-control studies for 2 reasons. First, we texted up to 20 potential controls for every enrolled case participant in anticipation of lower response rates for the web-based survey, inflating the number of contacted controls in our response rate calculations. Second, we did not follow up with all potential controls by telephone once our quota of 2 controls per case was reached. In contrast, telephone-only studies only call as many controls as needed to enroll the desired number of matched control participants, which is typically less than 20.

We found sociodemographic differences between participants completing the survey on the web and by telephone. Web-based respondents were more likely to be female, identify as White, non-Hispanic, have higher levels of education, and reside in urban areas, which was consistent with other studies evaluating survey mode effects [ 12 , 26 , 27 ]. Contrary to other studies that found higher web-based response rates among those younger than 35 years of age [ 14 ], participants aged 18-39 years in our case-control study were more likely to respond to the telephone survey, as were participants aged 60 years and older, participants working outside the home, and participants residing in areas with a higher burden of health injustices. Some of these differences may be attributable to the timing of when potential participants were contacted. While potential participants were texted a link to complete the web-based survey only in the morning, telephone interviews were administered throughout the day, including in the late afternoon and evening when more people may be at home and not working. In addition, older participants and participants in lower socioeconomic settings may experience more barriers to completing a web-based survey, such as limited internet access or less comfort using mobile platforms [ 15 ], making them more likely to complete a telephone interview.

While there were sociodemographic differences between web-based and telephone participants and between web-based and telephone case and control participants and their respective sample pools, the sociodemographic characteristics of combined web-based and telephone survey participants were broadly representative of the sample pools. This indicates that the sequential mixed-mode design allowed for the recruitment of more representative case and control participant groups than if we had used a telephone or web-based survey alone, and the use of this survey design can help reduce selection bias in case-control studies.

Telephone surveys conducted by trained interviewers have several advantages over other modes of administration. Most importantly, trained interviewers can answer participants’ questions, add clarifying questions, and probe interviewees for more complete responses, leading to better data completeness and quality. While increasing data quality, telephone surveys can lead to social desirability bias as participants may alter answers to questions to seem more favorable or socially acceptable to an interviewer [ 19 , 20 ]. An advantage of using a web-based survey is that the absence of an interviewer may provide participants with the opportunity to answer questions more candidly, potentially reducing social desirability bias [ 19 , 20 ]. While we found that web-based participants were more likely to report certain community exposures, most of the differential responses between web-based and telephone participants were no longer statistically significant after adjusting for variables shown to be associated with mode effects (age, gender, race, ethnicity, and geographic location). This suggests that demographic differences between web-based and telephone participants may be confounding variables and should be considered when analyzing and interpreting data for case-control studies.

Limitations

This project was subject to several limitations. First, cases were randomly selected from persons reported in Colorado’s COVID-19 surveillance system who had already completed an interview with public health, which may impact study findings. For example, this method of case-participant selection may account for the high enrollment rates we had for our case-control study, and these individuals may systematically differ from those testing positive for SARS-CoV-2 who did not complete an initial interview with public health. Second, sample pool data were obtained from the ELR system for control participants, which had incomplete demographic data. The sample pool characteristics presented in this paper may not be accurate because of these missing data and, in turn, affect our evaluations of sample representativeness. Third, the socioeconomic characteristics of participants may be subject to ecological fallacy as we used county-level Colorado EnviroScreen scores as a proxy for individual socioeconomic status. Fourth, it is unclear whether the systematic differences noted between web-based and telephone participants were due to the survey mode itself or due to the additional contact attempts made to enroll telephone participants. Finally, this sequential mixed-mode case-control study was implemented during the COVID-19 pandemic, a period marked by various political and social factors that could have influenced who responded to our survey and their responses. As such, findings from this paper may not be generalizable to case-control studies evaluating other diseases or outbreaks.

Conclusions

Telephone interviews conducted as part of an outbreak investigation are time-consuming and costly [ 8 ]. Given the limited resources and staff at many public health agencies, it is critical to find methods to increase efficiency and reduce the costs of outbreak investigations. Web-based surveys are more time- and cost-efficient than telephone interviews, greatly reducing the workload for health departments. However, web-based surveys may appeal to specific demographics, have lower enrollment rates, and may require a larger sample pool or a longer time to enroll participants, which may not be feasible for small outbreaks or ideal for public health emergencies when timely data collection is crucial.

By using a sequential mixed-mode design, we were able to efficiently recruit participants for a case-control study with limited impact on data quality. Moreover, using the sequential mixed-mode approach allowed for maximal sample representativeness compared to a web-based or telephone interview alone. This is critical during public health emergencies, when timely and accurate exposure information is needed to inform control measures and policy. While the sequential mixed-mode design allowed us to reach more potential control participants with fewer resources, we still encountered the same challenges recruiting control participants noted in other studies.

Acknowledgments

The authors would like to thank the following people for their contributions to the conception, design, or management of the case-control study: Nisha Alden, Andrea Buchwald, Nicole Comstock, Lauren Gunn-Sandell, Tye Harlow, Breanna Kawasaki, Emma Schmoll, RX Schwartz, Ginger Stringer, and Rachel K Herlihy. This project was supported by a financial assistance award from the Centers for Disease Control and Prevention and awarded to the Colorado Department of Public Health and Environment. The Colorado Department of Public Health and Environment contracted with EJSW at the Colorado School of Public Health. The content is solely the responsibility of the authors and does not necessarily reflect the official views of the Centers for Disease Control and Prevention or the Colorado Department of Public Health and Environment.

Data Availability

The data sets generated and analyzed during this study are not publicly available due to Colorado state statutes and regulations, which limit data release based on maintaining confidentiality for potentially identifiable person-level data, but are available from the Colorado Department of Public Health and Environment upon reasonable request.

Authors' Contributions

ADT contributed to the study’s conception, reviewed current research, performed statistical analyses, interpreted results, and was the primary author of the manuscript. AEW, MRT, and EJSW made significant contributions to the study’s conception and interpretation of results and critically revised the manuscript. RHJ and BAA substantively reviewed and revised the manuscript for its content. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest

None declared.

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Abbreviations

Edited by A Mavragani; submitted 19.01.24; peer-reviewed by M Couper, J Ziegenfuss; comments to author 13.02.24; revised version received 29.03.24; accepted 04.04.24; published 27.05.24.

©Amanda D Tran, Alice E White, Michelle R Torok, Rachel H Jervis, Bernadette A Albanese, Elaine J Scallan Walter. Originally published in JMIR Formative Research (https://formative.jmir.org), 27.05.2024.

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