It can be challenging to include people living in vulnerable circumstances and marginalised communities in research due to a lack of trust, time and reachability. Depending on the group, researchers may be perceived as the much-hated establishment, as spies, or simply as untrustworthy. Therefore, to plan the first contact and build trust is crucial before inviting people to participate in your study.

First contact could, for instance, be established through a trusted individual with similar experiences who can act as an intermediary. Such an intermediary can connect you to potential research participants. This approach to sampling is referred to as ‘snowball sampling’ and is considered a ‘non-probability method’.

Cartoon of one person connected to two people, them being connected to three people, and them being connected to many people.

Image source: (QuestionPro,2022)

Snowball sampling starts with a small number of persons who fit the research criteria,  e.g., mental health service users, refugees, homeless IV drug users. The researcher then asks each of these individuals to suggest several different individuals with the same characteristics among their acquaintances who will subsequently be contacted by the researcher to see if they would like to participate. Whoever volunteers for the study from this second stage, will be asked to do the same thing. Like a snowball, the sample grows with every round of interviews.

There are several downsides to snowball sampling that need to be taken into consideration:

  • the sample can be biased towards individuals who have many social connections and strong networks and excludes those who are more isolated
  • participants themselves may limit the sample by deciding who is ‘in’ or ‘out’ by acting as gatekeepers
  • it is difficult to guarantee privacy and confidentiality where participants select their friends and acquaintances

Nevertheless, snowball sampling is a solid sampling method especially when one has difficulty finding participants for a study.

(Author: Hanna Kienzler)

What is it?

Videos:

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Snowball sampling by Ibpsychsurvival (2019)

This YouTube video offers a brief introduction to what snowballing is and when it should be used. It also discusses the different types of snowball sampling including linear snowball sampling, exponential non-discriminative sampling and exponential discriminative sampling

(Academic reference: Ibpsychsurvival (2019, Sept 06). Snowball Sampling. [Video]. YouTube. https://www.youtube.com/watch?v=Z-P8dazQVi0)

Websites:

Snowball sampling: definition, method and examples by Simple Psychology (2012)

This webpage will introduce you to what snowball sampling is and the wider key terms needed to navigate this topic. Additionally in text format, it will explain the various types of Snowball sampling there are, a step-by-step guide on how to cluster sample and its advantages and disadvantages.

(Academic reference: Simple Psychology (2012). Snowball sampling: definition, method and examples. https://www.simplypsychology.org/snowball-sampling.html)

Articles:

Accessing hidden and hard-to-reach populations: snowball research strategies by Atkinson and Flint (2001)

This article explains how snowball sampling can be used to sample hidden populations that experience deprivation and social stigmatisation as well as hard-to-reach elites. It also describes some limitations of the technique and how it can be combined with other tools to enhance research success.

(Academic reference: Atkinson, R. & Flint, J. (2001). Accessing hidden and hard-to-reach populations: snowball research strategies. Social Research Update. https://sru.soc.surrey.ac.uk/SRU33.html)

Snowball sampling by Parker et al. (2019)

This article offers a balanced account of the advantages and disadvantages of snowball sampling as well examples of how it can be used and how obstacles can be overcome when using the sampling method. An inventive final section describes new techniques that have emerged in recent years thanks to social media platforms and other online tools.

(Academic reference: Parker, C., Scott, S. and Geddes, A. (2019). Snowball sampling. SAGE Research Methods Foundations. https://eprints.glos.ac.uk/6781/)

How is it done?

Videos:

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Snowball sampling | non-probability sampling (part-4) | NTA-UGC NET/JRF by Dr Sumeet Bakshi (2021)

This YouTube Video begins with an explanation of why the term “snowball” within snowball sampling is used. It offers an explanation of when to use it, examples of it and the main advantages and disadvantages. It will also provide you with a 3-step method of how to carry it out. This video is 5 minutes and 16 seconds in duration.

(Academic reference: Bakshi, S. (2021, August 20). Snowball sampling | Non-probability sampling (part-4) | NTA-UGC NET/JRF. [VIdeo]. YouTube. https://www.youtube.com/watch?v=GF3kBDb4wJs)

Websites:

Snowball sampling: definition, method, advantages and disadvantages by QuestionPro (2022)

This webpage begins with a description of snowball sampling and the different population groups it could be applied to researching. It also offers a detailed method of how to carry this technique out in practice. It also discusses some of its advantages and disadvantages.

(Academic reference: QuestionPro (2022). Snowball sampling: definition, method, advantages and disadvantages. QuestionPro. https://www.questionpro.com/blog/snowball-sampling/)

Snowball sampling by Laerd Dissertation (2012)

This webpage explains what snowball sampling is and the situations where it would be useful to use it. It will also provide you with a 2-step method of how to conduct snowball sampling.

(Academic reference: Laerd Dissertation (2012) . Snowball sampling.  https://dissertation.laerd.com/snowball-sampling.php#step1)

Method in action