Snowball Sampling

Snowball sampling is a sampling method used by researchers to generate a pool of participants for a research study through referrals made by individuals who share a particular characteristic of research interest with the target population. It is also referred to as chain sampling or chain referral sampling.

In snowball sampling, a subject from an initial sample group is asked by researchers to recommend individuals to act as future participants. The prompting for recommendations may take the form of an informal question, such as “Who are your best friends?” The subjects who are recommended by these individuals and agree to participate in the research are then considered to be the first wave of participants. The subjects in the first wave will be asked to make their own referrals of future participants. This second group of referrals will make up the second wave of research participants. This method may be repeated over and over again, thereby continuing the cycle, and just like a snowball rolling down a hill, the sample gets bigger and bigger.

Although the snowball sampling technique is applicable to a variety of study designs, it has been utilized most frequently in qualitative sociological research. In particular, this method has been employed in cases where the research focused on a sensitive issue, such as individuals who are HIV-positive, or when target subjects were difficult to locate in the general population. For example, snowball sampling has been particularly useful in research concerning deviant behavior, such as with participants who may be drug users or prostitutes.

Researchers’ use of the snowball sampling method has several unique advantages. First, due to the established familiarity between participants and those they refer, valuable social and interactional knowledge may be generated. Participants are observed within the context of their naturally formed relationships and social networks. Consequently, it may be easier to build rapport with referred participants, as researchers have already spoken with a friend, relative, or colleague at an earlier time.

The snowball sampling method also allows for the collection of both group and individual qualitative data simultaneously. For example, information may be gathered on group movements and routes of travel, in addition to individual backgrounds and histories. Utilization of the snowball technique allows researchers to overcome cultural boundaries such as lower literacy levels and language barriers, which may traditionally affect a participant’s likelihood of volunteering for a study.

Despite these advantages, there are also distinct limitations to snowball sampling. Due to the lack of randomization across study phases, data collected from participants cannot be considered generalizable to the target population as a whole. Definitive conclusions regarding the population may be inherently biased. For example, individuals [Page 1532]from the target group that are isolated from others may be less likely to be referred to researchers, thus excluding a subset of the population. This technique also introduces the potential for a lack of confidentiality across participants. Researchers may be asking participants to disclose personal or sensitive information about others related to target group membership. Referred participants are then faced with the decision of whether to disclose their eligibility status to the researcher.

...