Sample size for Qualitative Interviews

Identifying your sample
Through the looking Glass

This is one of life’s great mysteries and one that has troubled many a qualitative researcher. How many interviews are enough before i have enough data? What should be my sample size for Qualitative Interviews? During my research this was a issue I really struggled with and found that justifying a sample size was not an easy task and required me to juggle multiple variables.

This short post covers some of the key considerations researchers need to consider and the issue of data saturation and the sample size for Qualitative Interviews.

Justification of Sample

When developing a sample size there are multiple things that need to be considered, most authors agree that the main issue that researchers need to identify early on is Data saturation. The researcher in determining if they have arrived at data saturation should ask themselves:

  • Have I hit the peak of my data?
  • Have I collected so much data that no new phenomena will now emerge?
  • Have I missed anything?

The flipside to data saturation is data overload, I once met a PHD student who administered over 35 in-depth interviews which each lasted over an 1 hour and 30 mins long. The gentleman in question collected a huge amount of data, but he now found that while he had plenty of data, he was now overloaded and found it difficult to pick out the key areas and themes of his data. He struggled to break down the key aspects.

Ritchie et al. (2003), suggests that within qualitative research the sample size is usually small primarily because phenomena only need to appear once to be part of the analytical map. After a while there is a point of diminishing return when increasing the sample size no longer contributes to new evidence. Diminishing return is a problem that occurs depending on the type of data being collected, Crabtree & DiCicco-Bloom (2006) refer to this process of diminishing return as data saturation and a signal that the data collection process is now complete or near completion.

In the view of Guest et al. (2006) data saturation can occur within the first twelve interviews and after that very few new phenomena are likely to emerge. In the view of Gonzalez (2009) when undertaking research that is reliant on a phenomenological approach, the sample size is usually driven by the need to uncover all the main variants within the approach, he suggests that within conditions such as this, small survey samples of less than twenty are common. Finally the view of Creswell (2011) in relation to sample size is that normally within qualitative research it is typical “to study a few individuals or a few cases” (pg. 209).

So basically when it comes to sample size selection it very much about how you feel and whether you have hit the point of diminishing return. Personally I feel that within a qualitative interview based on a phenomenological approach it is not uncommon to see samples sizes of between 15-25. 

If you would like to discuss this in more detail or you would like to add anything please leave a comment below.


Legard, R., Keegan, J., & Ward, K. (2003). In-depth interviews. In J. Ritchie & J. Lewis (Eds.), Qualitative research practice: A guide for social science students and researchers (pp. 138–169).

B. F., & DiCicco-Bloom, B. (2006). The qualitative research interview. Medical Education, 40(4), 314–318.

Guest, G., Bunce, A., & Johnson, L. (2006). How Many Interviews Are Enough?: An Experiment with Data Saturation and Variability. Field Methods, 18(1), 59–82. doi:10.1177/1525822X05279903

Gonzalez, C. (2009). Conceptions of, and Approaches to, Teaching Online: A Study of Lecturers Teaching Postgraduate Distance Courses. Higher Education, 57(3), 299–314. doi:10.2307/40269124

Creswell, J. W. (2011). Educational Research: Planning, Conducting, and Evaluating Quantitative and Qualitative Research. (Fourth.). Pearson.


27 thoughts on “Sample size for Qualitative Interviews”

  1. My data is secondary data which is annual accounts in SMEs. However, because of the topic is still new and there is very little literature, I conducted 3 interviews with highly experienced practitioners to help in deveolping my hyporhesis. So the interviews work together with the literature to reach my research hypothesis. After that I will start collecting and analysing my data.
    Do you think that only 3 interviews can be considered enough?


    1. Hi Abbas,

      Thank you for your comment. The main issue with your data is do you feel that you have reached data saturation? In your interviews have you covered all the key areas. Finally, does your interview data correlate with your secondary data? If so and you are comfortable with your data then you may have enough. Personally, I would do maybe one or two more to ascertain that you have covered all aspects and there is evidence of saturation. Whatever you decide, good luck.


  2. Dear Dr. Abdul Jabbar
    Many thanks for the valuable information. You mentioned “Ritchie et al. (2003)”, it is not available in the references. Can you provide this reference, please?


    1. Hey Maryam, Thanks for pointing this out. The reference is:

      Ritchie, J., Lewis, J., & Elam, G. (2003). Designing and selecting samples. In J. Ritchie & J. Lewis (Eds.), Qualitative research practice: A guide for social science students and researchers (pp. 77–108). London: Sage.

      Hope this helps.


  3. Thanks Abdul.

    The area I am researching is politically sensitive and hasn’t been researched before. I am doing exploratory research and am redrafting my methodology chapter to help justify why I have only 16 interviews (13 different respondents). I am creating local theory but I am nervous that I might get an external examiner at my viva who is more quantitatively focused. I am therefore looking for published articles with only a handful of interviews. Whilst I have found a few useful leads from this URL –
    I wondered if you knew of any articles that would fit the above description.

    Thank you in advance.



    1. Hey Frank, Thanks for the comment. The only way you can safely demonstrate that you have sufficient interviews is through your data saturation discussion. Can you prove that you have saturated your data? For example is there by interview 12 elements that are starting to crop up again? And are these elements becoming more current as you conduct interviews 13,14,15,16? With profs who are into Quants its all about what you can prove and data validity. So maybe read up on that in a little bit more detail. Remember Gonzales says that less than 20 is common in qualitative research. Whatever happens good luck!


      1. dear sir,
        i just want to know whether can we do a qualitative research within 1 month period of time?


      2. Hey Nygil,

        Thanks for getting in touch. Before I can advise you in this respect can you please answer the following questions:

        1 – How many interviews have you done/intend to do?
        2- Have you transcribed those interviews
        3- How long are those interviews?
        4- What is your analysis approach.

        Many thanks


  4. Dr. Jabar when you say that a sample size of 15-25 is sufficient are you accounting for multiple interviews with each person. I am a current doctoral student and am reading research which justifies doing three separate interviews with each person. So I am just trying to get some clarification.




    1. Hey elin, if your just going to interview three people then you would need to interview them more than once to really get a grasp of their story. I know a person who interviewed only 5 people and she collected nearly 40 hours of interview audio. She used IPA with a narrative enquiry.

      I hope this helps


  5. Hi Dr. Abdul

    Thanks for this, it really helps. I’m currently enrolled for a research based masters and I have one question l was hoping you could perhaps help clarify a bit. I’m conducting research on a maturing domain (South Africa) and not so many people/organizations in the country have specialized knowledge in the field. My initially plan was to conduct interviews but l’m facing resistance from my targeted participants, who instead prefer a questionnaire approach. I have collected about 10 responses so far, do you think this sample size may be acceptable, in light of all the rejection l’m getting and tight deadlines to complete this research? How can l motivate this?


    1. Hey Robert,

      Many thanks for your comment. A questionnaire approach with 10 responses is in my view not enough. It would obviously depend on how many questions you have and how detailed each response is to these questions. Your other issue is your analytical approach, this maybe severely impacted by what is such a small sample. I hope you manage to find a solution to your research collection, but it does sound like you are in a bit of a pickle!


  6. Dear Dr. Jabbar
    I have 3 groups with 3 participants in each group to be interviewed separately. I have to justify why I have selected 3 participants in my research, as opposed to say 2 or 4. I am also interviewing each participant twice, with each interview covering different topics and a gap task set. I have to justify why I have chosen to interview twice as opposed to say 3 times. Data saturation can come into it, but I need to give a consideration before doing the research. Any ideas – my head is so fuzzy, and I have done so much reading on the area?


    1. Hey Leo,

      There is a lot to unpick here. Essentially in my view you are interviewing nine individuals, when you say groups are you conducting focus groups? Or have you split the interviewees into smaller chunks for brevity? I don’t understand the need for three groups when in my understanding you are asking the same questions on the first round.


      1. Hello, Dr Jabber. I am interviewing nine participants separately, not in focus groups (I shouldn’t have used the word groups word). Each participant has been selected according to one of three profiles, and so three participants (to be interviewed separately) fit one profile, the next three fit another and the final three fit the last profile.


      2. So rather than actually justify your actual respondents I would justify the profiles and why they apply to those specific individuals. A matrix diagram may help in pushing this information together, nd visualise what it is you are trying to do.


  7. Dear Dr Jabbar:
    I wish to use purposive sampling to interview 4 persons individually and conduct a separate focus group of 6-8 persons in a gated community to determine what causes cohesion in such a community and ways to improve communication. Do you think I am sampling enough persons?


    1. If you link your focus groups to your individual interviews then yes. A lot will depend on how many focus groups you carry out. If only one then I don’t think this would be enough. Sorry for the late reply!


  8. Hi,
    I’m about to do my sociology undergraduate dissertation, and I was wondering if 10-15 semi-structured interviews would be sufficient?
    I have a pretty fixed timeline to follow, so I want to have decent time to analyse my data.

    Liked by 1 person

  9. Hi Dr., I found the sharing here extremely useful.
    could you share your opinion about using the data from diferent groups of interview participants to triangulate the data collected? for example, you interview both service providers and customers.

    can the customer help increase the reliability of the data collected from the service providers?

    Thank you!


    1. Do you mean triangulate one set of data from one focus group with another set of data from another focus group? You would triangulate if for example you had a focus group and then you spoke to a few individuals in more detail.

      Customers in your case would help to give you a deeper insight from a different perspective but any triangulation would need to hinge on your framework.


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