Snowball sampling is a recruitment technique in which current research participants are enlisted to help recruit other potential study participants. This involves tapping into each participant’s social network to find more subjects for a study. It allows researchers to find subjects who belong to a specific population who might not otherwise volunteer or seek out study participation.1
As the name suggests, snowball sampling starts small and slowly “snowballs” into a larger sample. It is sometimes referred to as chain sampling, referral sampling, respondent-driven sampling, or chain-referral sampling.
At a Glance
Snowball sampling is a non-probability method allowing researchers to tap into hard-to-reach populations. Often used in qualitative designs, it allows researchers to recruit participants through referrals. This can be beneficial because it helps connect researchers with individuals they might not otherwise reach, but it can also contribute to sample bias and make it difficult to generalize the results to a larger population.
When to Use Snowball Sampling in Psychology Research
In most cases, researchers want to draw a sample that is both random and representative. Random selection ensures that each member of a group has an equal chance of being chosen, while representativeness ensures that the sample is an accurate reflection of the population as a whole.
While ideal, getting a random, representative sample isn’t always possible. In such cases, researchers might turn to another method such as snowball sampling.
There are a number of situations where snowball sampling might be appropriate. These include:
- When researchers are working with populations that are difficult to reach, including marginalized or hidden groups, such as drug users or sex workers2
- When research is in the exploratory stage, and scientists are still trying to learn more about an emerging phenomenon
- When researchers are working to generate a hypothesis before they conduct more comprehensive studies
- When recruiting through social networks makes the most sense in terms of cost and available resources
- When researchers are studying communities that are highly connected via shared characteristics of interest
Is Snowball Sampling Qualitative or Quantitative?
Snowball sampling is commonly used in qualitative research.3 It uses a non-probability sampling method and is often used in studies where researchers are trying to explore different psychological phenomena and gain insights. Sample sizes may be smaller in this type of research, but often results in contextually-rich data. This can help researchers understand the nuances of what they are studying in a specific population.
How Snowball Sampling Works
Snowball sampling starts by finding a few individuals who meet the necessary criteria for a research sample. These individuals are sometimes known as the “seeds.” The researcher then asks each participant to provide the names of additional people who meet those criteria.
The seed participants are interviewed and provided with a reward for their participation. They may then be given “coupons” that they can give to other eligible individuals. Each coupon contains information that allows recruiters to trace its origins. Potential participants can then redeem these coupons by enrolling in the study.1
Each individual approached for participation is also asked to provide information on potential candidates. This process is continued until enough subjects have been located.
Pros and Cons of Snowball Sampling
Snowball sampling can have some pros and cons. Before using this approach, researchers should carefully weigh the potential advantages against the possible disadvantages and be transparent about any resulting limitations of the findings.
Advantages of Snowball Sampling
Snowball sampling can be particularly important when researchers are dealing with an uncommon or rare phenomenon. Traditional recruitment methods might simply not be able to locate a sufficient sample size.
It can also be helpful when participants are difficult to locate. This can include situations where people might be reticent about volunteering information about themselves or identifying themselves publicly. Because snowball sampling relies on recruiting people via trusted individuals, people may be more willing to participate.
Because snowball sampling provides essential information about the structure of social networks and connections, it can also be a helpful way of looking at the dynamics of the group itself.
Limitations of Snowball Sampling
The problem with snowball sampling is that it can contribute to bias.4 The opinions and characteristics of the initial members of the sample influence all of the subsequent subjects who are chosen to become part of the study.
This can make it more difficult for researchers to determine who might be missing from their sample and the factors contributing to that exclusion. Some variables might make it less likely for certain people to be referred, which can bias the study outcomes.
Another problem with snowball sampling is that it is difficult to know the size of the total overall population. It’s also challenging to determine whether the sample accurately represents the population. If the sample only reflects a few people in the group, it might not be indicative of what is actually going on within the larger group.2
Research suggests this sampling method can be a cost-effective way to collect data. However, researchers also caution that it can introduce bias, which means that caution must be used when interpreting the results of studies relying on snowball sampling.5
Examples of Snowball Sampling
To understand how snowball sampling can be used in psychology research, looking at a few different examples can be helpful.
LGBTQIA+ Youth
Imagine a study where researchers want to investigate the experiences of LGBTQIA+ youth who live in rural areas. Because this population might be more difficult to reach due to discrimination, researchers might start by recruiting participants through local LGBTQIA+ organizations. Once they have an initial sample, the researchers can ask the current participants to introduce them to other people who are also LGBTQIA+.
Mental Health of Specific Populations
Consider a situation where researchers want to study the mental health of people in a particular profession, such as first responders who work in high-stress settings. The researchers might start by recruiting participants through professional organizations and then ask participants to refer them to colleagues who might also be interested in taking part.
Online Communities
Researchers might interested in learning more about phenomena that affect people who belong to specific online communities. They might reach initial participants by contacting them through online forums or websites and then ask if these participants are willing to share contact information for other members of the community.
Steps to Conduct Snowball Sampling
To conduct a snowball sample, researchers often use the following steps:
- Create a research question and define the objectives of the study.
- Identify the initial participants based on specific pre-determined criteria.
- Obtain informed consent that clearly explains the purpose, benefits, and potential risks of participating in the research.
- Collect data from the initial participants using surveys, interviews, observations, or other techniques.
- Ask participants to refer you to other potential participants and obtain contact information if possible.
- Contact the potential participants who have been referred to you. Explain the study and invite them to participate.
- Repeat the same process with each subsequent participant.
- Continue the process until a sufficient sample has been obtained.
The Role of Snowball Sampling in Modern Research
While snowball sampling has its limitations, it plays an important role in modern psychology research. In particular, it can help researchers make contact with vulnerable or marginalized populations who are often overlooked and left out of more traditional sampling methods.
This technique can help researchers connect with the members of communities who may be hesitant to participate due to discrimination or the stigma associated with their condition.
It can also be a way for researchers to investigate phenomena that may be newly emerging and that might not yet be detectable using other sampling techniques.
Given the importance of social networks in today’s highly connected work, snowball sampling also gives researchers a unique opportunity to examine how individuals connect to their communities. Researchers can use the information they collect to re-trace connections, providing valuable insights into how relationships and social dynamics affect the phenomena they study.3