Snowball effect: advantages, disadvantages, implementation

The snowball effect is a sampling method used in qualitative research. It facilitates the recruitment of respondents in difficult contexts. The sampling carried out thanks to the snowball effect has advantages but also limitations that we discuss in this article. You will also find an exhaustive definition as well as concrete examples. If you would like more information about the qualitative studies we carry out, please do not hesitate to contact us.


  • What is the snowball effect?
  • Implementation
  • Advantages
  • Disadvantages
  • Examples
  • Conclusion

What is the snowball effect?

The snowball effect is a technique for recruiting respondents for focus groups or individual interviews. It is therefore a sampling method for qualitative research.

The snowball effect consists of asking each person contacted for the contact details of one or more other people to be interviewed. With each contact, the list of potential respondents grows like a snowball that grows continuously when pushed. This step can be implemented directly during the first contact (before the interview) or after the respondent has been interviewed.

The snowball effect is easy to implement, which explains its success. It is an alternative to more complicated approaches such as participatory observation. Anthropologist Teen Vote, for example, lived with the homeless for the purposes of his research.

It is therefore easy to understand that this is a non-probability sampling method. The snowball effect does not in fact make it possible to construct “representative” samples, even if the notion of representativeness in qualitative research does not really make sense (we refer you on this subject to our article on memoir ghostwriters as well as to our qualitative sample size calculator).


If you decide to take advantage of the snowball effect, you can implement it in 2 ways:

  • either by asking directly for contact details
  • either by asking for contexts, relays, places through which to get in touch with other respondents

Practically, here are some ideas of questions to ask when you contact potential respondents or at the end of your qualitative interview / focus group. Proceed as follows.

1) First recall the context of your study

“As a reminder, my study focuses on studying [description of objectives]. In this context, I would like to interview people who [description of the profile of the ideal respondent]”

2) Ask for contacts of other respondents

“No doubt you know people who fit this description. You could really help me by putting me in touch with them”

3) Expand the request if you don’t get a direct response

“Perhaps then you can give me some ideas for finding such people.” Can you give me the contact details of anyone who might know such people? »

4) Make people think about places or ways to get in touch

Provided you haven’t already asked this question during the interview, get your respondent to think about the places (physical or virtual) where you might find other respondents.

“If you had to find guarantors, where would you look for them? »

Advantages of the snowball effect

The snowball effect has several advantages that we analyze in this paragraph.

Ease of implementation

Recruiting respondents in qualitative research is usually a very complex part. It is at this stage that the very feasibility of the study comes into play. No respondents = no interviews or focus groups.

The snowball effect is an approach within everyone’s reach, easy to apply, to increase the probability of success in the recruitment phase. This is undoubtedly what explains its popularity.

The only applicable method to reach “hidden” populations

The snowball effect is often touted as the best sampling method for hidden populations. A population is said to be “hidden” when it is difficult to access, when its members are poorly connected to other communities. These are therefore typically populations that can be described as marginalized. The examples we cite at the end of this article of the extent of this marginalization: drug addicts, homeless, and sick, unemployed.

However, “hidden” populations are not limited to those who are marginalized in the negative sense of the term. At the other extreme of the spectrum, the wealthiest for example also live in hiding and are difficult to access (see a concrete example here). Having a recommendation, a common contact, is often essential to approach them. The snowball effect is perhaps in this case the only way to constitute your sample.

Understand the relational dynamics within a population

Nay (2008) suggests another advantage after 2 studies using the snowball effect. The first dedicated to backpackers, the second to professional drivers in Jerusalem. In both cases, the author based himself on individual interviews with 2 hard-to-reach populations and reflected on what the snowball effect taught him about the populations he was studying. He writes:

As I first looked for information in the material produced by the interviews in this research (i.e. the “text”), I then realized that I could learn a lot about backpackers and men marginalized by reflecting on the dynamics of gaining access to them or approaching them. It is this idea, and the interrelationships that then emerged between sampling and maintenance procedures in these projects, that led me to re-evaluate the role of sampling via the snowball effect.

While I initially looked for information in the material produced in the interviews in these researches (i.e., the ‘text’), I later realized that I could learn a great deal about both backpackers and marginalized men by reflecting upon the dynamics of accessing or approaching them. It was this insight, and the interrelations that then emerged between the procedures of sampling and interviewing in these projects, that led me to re-evaluate the role of snowball sampling

Disadvantages of the snowball effect

Before using the snowball effect technique, it is important to understand its limits.

Diversity bias

Since the snowball effect is a non-probabilistic technique based on existing relationships between respondents, this may result in a problem of diversity of opinions expressed. The popular adage indeed says “birds of a feather flock together”. This similarity of opinion among respondents can be seen in the field.

By asking respondents to tell you about people to interview, you risk ending up with a sample that expresses similar opinions. This lack of diversity necessarily constitutes a bias.

The conduct of the interview determines the result

The quality of the contacts provided by the people you have interviewed depends on the relationship you have managed to build with the best ghost writing. In other words, if you manage to establish a good relationship with your respondent, the qualitative interview will go well. As a result, you will have more chances of recovering interesting contacts for the rest of your study.

The snowball effect, as a sampling method, is therefore potentially based in part on the quality of the human relationship that you have managed to build.

Loss of control

Unlike other sampling methods, the snowball effect leads to a loss of control for the person carrying out the qualitative research. In effect, the recruiting effort is “shifted” onto the respondents. To account for this loss of control, it is useful to keep a written and/or visual record of the recruitment process (see graphic above).

Examples of the use of the snowball effect in qualitative research

Here are some examples of how to put the snowball effect into practice in qualitative research. We start by giving you some cases that we have covered within our market research agency, then continue with examples from the academic literature.

Study on private bank customers

Clients of private banks must prove that they have a minimum amount of assets and significant outstanding. Their level of wealth therefore makes them a population limited in size. These clients also tend to be very discreet, which complicates their approach.

The study we conducted for a large Luxembourg bank therefore relied on the snowball effect in order to collect recommendations for approaching respondents.

Study on the visually impaired

We have conducted several studies on the needs of visually impaired people. This population suffers from a lack of integration within society in general and the world of work in particular (on this subject, see our report for Parliament on the employment of disabled people in the administration).

In order to approach these populations, we notably relied on the administrators of specialized online forums to obtain the contacts of potential respondents.

Academic studies

Examples of academic research using the snowball effect are legion:

  • drug users: Hackathon (1997) , Sifaneck & Neighs (2001)
  • unemployed: Atkinson & Flint (2001) , Fauquier & Sergeant (1997)
  • were you painted PAGE : Sifaneck & Neighs (2001)
  • elderly: Warren & Levy (1991)


The sampling method based on the snowball effect is a classic in qualitative research. It is particularly suitable for carrying out qualitative interviews with hidden populations.
However, its ease of implementation should not overshadow its limitations. The snowball effect can in fact lead to selection biases and less diversity in the opinions collected.

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