The “how many” question regarding participants in a case study using in-depth interviews is contentious since the sample size depends on many factors such as, among others, the study scope, topic nature, and data type. In fact, there is variability in what is proposed as a minimum. Most relevant literature recommends anywhere from 5 to 50 participants could be enough. Here is a relevant piece.

Dworkin, S. L. (2012). Sample size policy for qualitative studies using in-depth interviews. Archives of Sexual Behavior, 41(6), 1319-1320. https://doi.org/10.1007/s10508-012-0016-6

The number of participants depends on the nature and scope of your study.

The classic strategy for determining the number of interviews in a qualitative study is saturation, i.e., the point at which no new information is being produced by your interviews. Of course, there is no way to predict this in advance, but if the information you are getting becomes repetitive after 15 interviews, then there is no point in conducting 10 more.

The number of interviews depends on the subject matter.

However, studies that have been published in journals indexed in Web of Science and Scopus usually use around 15 interviews. Of course, this also depends on the saturation. Alam, M.K. (2020), indicate that a sufficient number of participants is 10-20 .Roselle, A. (1996), " recommends 6 to 20 participants.

Roselle, A. (1996), "The case study method: A learning tool for practising librarians and information specialists", Library Review, Vol. 45 No. 4, pp. 30-38. https://doi.org/10.1108/00242539610115281

Alam, M.K. (2020), "A systematic qualitative case study: questions, data collection, NVivo analysis and saturation", Qualitative Research in Organizations and Management, Vol. 16 No. 1, pp. 1-31. https://doi.org/10.1108/QROM-09-2019-1825

The Number of interviews samples depends on many factors, mainly research purpose, also depends on the saturation and nature of data.

Participants in qualitative method depends on saturation point where you feel data redundancy has been started.

Please take a look here into the methodological section:

Kristal, S., Baumgarth, C., & Henseler, J. (2020). Performative corporate brand identity in industrial markets: The case of German prosthetics manufacturer Ottobock. Journal of Business Research, 114, 240-253.

In depth interviews are an excellent way of gathering information. I think 6-10 is a good number but the exact number remains contentious!

Actually there is no hard-fast rule of this

Selection of sample depends on size of population. Always need to study 10% sample for good result of research.

The data saturation usually determines the number of participant, therefore is not feasible to be exact with the actual number before han. I would recommend between 10 and 15 interviews, Adding one or two key informants might be beneficial.

According to Creswell adequate sample size ranges between 20-30 participants (Creswell, 1998)while other authors suggest between 5-50 participant is adequate.

Previous responses concerning saturation are all correct. As a rough guide, I would expect 10 - 15 interviews would be needed to achieve saturation. The reason why a single interview would be regarded as inadequate is that you have no idea whether the data gathered adequately covers the subject under analysis. Also, you do not mention how you plan to analyse the interview data; simply repeating what one person has told you is unlikely to lead to a successful dissertation!

the number of interviewees for a single case-study research is not predetermined since this is a qualitative type of research. Since the research design is characteristically exploratory, it will be advisable for the researcher to rely on the saturated (point of fact repetitions) nature of the data collected. At that point the number reached could be the sample size. Practically and objectively, it is always difficult to know whether or not the researcher has reached a saturation point. Hence, it requires some amount of discretion and tactfulness.

Interviews may be an important part of you single case study. However, I find that supporting literature (peer reviewed of course) are more essential than interviews because they have already been peer reviewed. If you find supporting literature to support your single case study, then your interviews (even one) support your study, but you must have significant published literature (i.e., 40+ references).

Good luck.

Te recomiendo que consultes a @Muñiz, Manuel. (2010).

Delimitar el estudio de caso a una sola unidad, no quiere decir que sea una sola opinión, en tu estudio debes revisar la población afectada o influenciada y tenerlos en cuenta a la hora de las entrevistas o de las encuestas, espero que te sirva este dato y te deseo éxito en tu investigación.

I agree with David L Morgan, and Thobeka Sweetness Nkomo.

Single case study via purposive sampling requires identification of one or a few experienced practitioners and/or experts in the area that you are investigating to elicit data from, via rigorous in-depth interview, coupled with certain triangulations such as analysis of relevant work documents and observations of work processes and procedures. The transcribed and coded interview data will generate findings in the form of emerging themes which must then be verified by the respondent themselves (called member -check) and also by experts in the field of study. Data saturation is the key for the data elicitation and probing to be considered sufficient.

In addition to the Interview(s) it would be good idea to have a theme based survey on the subject you are researching. Survey response can be obtained from various stakeholders to get diverse viewpoints and also to triangulate the response you receive from the Interview(s).

First of all, I would like to thank everyone who took the time and provided an answer to my question. This shows the great level of support provided by the community here at Research Gate.

I am going to share my final approach as this may help other people (students) who would have similar doubts when they conduct their research.

I would like to start off by addressing my research strategy clearly. The research is designed as a single-case study. As I mentioned in my question, the interest is to investigate the process in state-owned enterprises (SOEs). As a result, one SOE has been selected for the investigation. This supports the argument of representativeness and typicality as highlighted by Yin (2009) as well as the exemplification which is highlighted by Bryman (2008). The main data collection approach is documentation and interviews.

I had an issue with my interviewing approach, in which I had to post the question here. As can be shown from answers here, one interview with one person is never sufficient.

The final interviewing approach is the following; I have identified three main phases to be investigated across the studied case (SOE). Through purposive sampling, I have identified one representative from each phase. Of course, these phases are linked to each other, in which then will allow more comprehensive data for analysis, as well as reducing the bias. While a sample size of only three people may seem small, however it is sufficient given that documentation that are provided will explain real-life events and would be tested against data from interviews. Also, the documents have been previously audited and authorized by the concerned departments.

I had to mention everything in the methodology chapter with clear justification (including philosophy, approach to theory, etc.) and I have prepared a case study protocol as well, which will be attached in the appendix.

The gathered data will then be tested against my findings from the literature.

Finally, I would like to thank everyone again, and I wish anyone who will be conducting a research for a dissertation as I am now, the best of luck.

I do not agree that one interview per phase is enough. What if you interviewed a second person and they completely disagree with the first?

There is no specific number to interviewees in a qualitative research. However, literature suggests 10 to 50. At masters level at least 6 would do. One can not employ a thematic orientation with a single interview. You may add questionnaires at the level of a descriptive statistics, and still remain within the parameters of a qualitative research study.

Hello Yousef, I recommend you to consider what is recommended in the literature, regarding the saturation of information. Ideally, as you collect the information it is analyzed. According to the results of the analyzes that you carry out, the need for more interviews is identified.

In the following article I used thematic analysis and focus was used as a source of information:

Article Experiencias Desmotivacionales y Motivacionales de Estudiant...

I also recommend you review the following work:

Article Emociones en Educación Matemática: una mirada con base en el...

at master's level, i would recommend minimum six interviews to 12 is recommended applying purposive sampling

Dear Yousef Samir I agree with David L Morgan, and Thobeka Sweetness Nkomo.

I agree with David L Morgan. However, it is largely dependent on the nature and scope and design of a study.