Sampling refers to the practice of selecting a subgroup of people from a defined population to include them in a study. In qualitative research, the aim is to select people who can provide different perspectives and experiences relevant for the study topic. Including different, even contradictory, viewpoints is important to generate a complex understanding and ‘information-richness’ about the research topic.

Take, for example, a study in which a researcher aims to understand the impact of war and trauma on the mental health and wellbeing of refugee women. To gain in-depth insight into the women’s situation, the researcher might want to include people with different perspectives on survivors’ mental health in the study. These could include:

  • women survivors of war
  • family members
  • humanitarian aid providers
  • mental health and psychosocial support workers
  • community leaders and organisers

Creating a sample like this is referred to as ‘purposeful sampling’. When creating a purposeful sample, researchers pre-define which types of participants can provide valuable views for the research objective. In other words, the ‘researcher exercises his or her judgment about who will provide the best perspective on the phenomenon of interest, and then intentionally invites those specific perspectives to the study’ (Abrams, 2010, p. 538).

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Key assumptions about qualitative samples: 

  • the sample is usually relatively small, ranging from five to 20 participants (it can be smaller or larger than this depending on the study)
  • people included in the sample are not assumed to share the same experiences or viewpoints. In other words, they cannot ‘stand-in’ for one another
  • the particular experiences and perceptions of participants are of interest. So-called ‘outliers’ or ‘special cases’ are insightful as they can add complexity and depth.

Assessment of an Optimal Qualitative Sample

To assess whether your sampling procedure is optimal, you can ask yourself the following questions:

  1. Is the sampling strategy relevant to the conceptual framework and questions addressed by my research?
  2. Is my sample likely to generate rich information on the type of phenomena which need to be studied?
  3. Is it likely that my sample produces believable descriptions and explanations?
  4. Is my sample ethical?
  5. Is my sample feasible?

[Questions adapted from Miles and Huberman (1994)]

In summary, the approach to sampling must match your research objective and questions as well as your overall study design. It needs to be carefully developed for valuable data to emerge as part of your research.

(Author: Hanna Kienzler)

What is it?

Blogs:

Sampling considerations in qualitative research by Daniel Turner (2016)

This blog goes into depth on some popular methods of qualitative sampling and cites a variety of other useful sources along the way. It explores some of the implications of various sampling techniques for the diversity of your sample and the representation of relevant groups.

(Academic reference: Turner, D. (2016). Sampling considerations in qualitative research. Quirkos Qualitative Research Blog.   https://www.quirkos.com/blog/post/qualitative-sampling-issues/)

Websites:

Qualitative research sampling methods: Pros and cons to help you choose by Edanz Learning Lab (2022)

This page begins by explaining how to choose the right sampling method for your research. It then offers insight on various sampling methods, including; what they are, when to use them, and their advantages and disadvantages in practise.

(Academic reference: Edanz Learning Lab. (2022). Qualitative research sampling methods: pros and cons to help you choose. Edanz Learning Lab.   https://learning.edanz.com/qualitative-sampling-methods/)

Books:

Sampling in qualitative research by Musarrat Shaheen, Sudeepta Pradhan and Ranajee Ranajee (2019)

This book chapter offers insight into the range of qualitative sampling techniques available, beginning with a description of theoretical sampling and then purposeful sampling. The authors then outline how purposeful sampling acts as a source for other samples and offer descriptions of each one. The chapter goes on to offer guidance in understanding at which point data collection may stop. After reading the chapter there are some questions you can quiz yourself on – the answers are located below.

(Academic reference: Shaheen, M., Pradhan, S., & Ranajee,. (2019). Sampling in qualitative research. In M. Gupta, M. Shaheen, & K. Reddy (Ed.), Qualitative techniques for workplace data analysis (pp. 25-51). IGI Global.)

How is it done?

Videos:

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Sampling for qualitative research by Driz Teaches (2020)

This YouTube video offers insight into how to conduct sampling for qualitative research. As well as why non-probability sampling is used to do qualitative research and a detailed explanation and assessment of the following sampling methods: quota sampling, expert sampling, snowball sampling and convenience sampling. This video is 16 minutes and 30 seconds long. (Academic reference: Driz Teaches (2020 December 29). Sampling for qualitative research [Video]. YouTube. https://www.youtube.com/watch?v=RvEZPZPsG3g)

Websites:

10.2 Sampling in qualitative research by Scientific Inquiry In Social Work (2022)

This webpage offers insight into what non-probability sampling is and when it might be used. It also offers insight into the different types of non-probability sampling.

(Academic reference: Scientific Inquiry In Social Work (2022). 10.2 Sampling in qualitative research. Pressbooks. https://scientificinquiryinsocialwork.pressbooks.com/chapter/10-2-sampling-in-qualitative-research/)

Books:

Sampling and choosing cases in qualitative research: A realist approach by Nick Emmel (2013)

This book  starts by offering some historical insights into the origins of qualitative sampling and its connection to grounded theory and the significance of it to the topic. The author also discusses how to choose your sample in line with this.

(Academic reference: Emmel, N. (2013). Sampling and choosing cases in qualitative research. Sage.)

Method in action

Articles:

Sampling for qualitative research by Martin N. Marshall (1996)

This article distinguishes qualitative sampling methods from those used in quantitative research and explains the benefits of three broad approaches to qualitative sampling (purposeful sampling, convenience sampling and theoretical sampling). The author draws on examples from their own research to highlight how qualitative sampling works in practice. This would help you develop broad understanding of what qualitative research looks like.

(Academic reference: Marshall, M.N. (1996). Sampling for qualitative research. Family Practice, 13(6), 522–526. https://academic.oup.com/fampra/article/13/6/522/496701)

Reports:

Designing sampling strategies for social qualitative research: With particular reference To The Office For National Statistics Qualitative Respondent Register  by Wilmot, A. (n.d)

This report paper will allow you to understand how a strong sampling framework is made within qualitative research and why it is needed. Additionally, it draws upon qualitative data from the Office for National Statistics to assess how a sample frame can be constructed for qualitative research. The Office for National Statistics is an independent organisation that collects data relating to wider society on both the local and national level.

(Academic reference: Wilmot, A. (n.d). Designing sampling strategies for social qualitative research: with particular reference to the Office for National Statistics Qualitative Respondent Register. Office For National UK Statistics. https://wwwn.cdc.gov/qbank/Quest/2005/Paper23.pdf)