Source: Boise State University IRB
Snowball Sampling Recruitment Method
Snowball sampling is a recruitment technique in which research participants are asked to assist
researchers in identifying other potential subjects. For example, a researcher seeking to study
patterns of informal leadership in a community may ask individuals to name others who are
influential in a community. The use of currently enrolled research participants to recruit
additional research participants (sometimes referred to as “the snowball sampling”) may be
approved by the IRB under some circumstances. However, the protocol must include
justification of the use of this method in the context of the study and target population.
Consideration of minimal risk is likely to play an important role in IRB review of snowball
recruitment procedures. For example, it would make a big difference whether the research
involved extramarital affairs or substance use as opposed to family meal time routines or
leisure activities. To “cold call” someone on sensitive topic issues places him or her in a
potentially embarrassing situation, which should be avoided. Moreover, the original subject is
being placed in the position of being asked to disclose information about a third party without
that party’s consent.
Snowball recruitment where the researcher obtains names and contact information from one
individual for another one, particularly for research involving sensitive topics, is generally not
considered appropriate.
Using such a method could result in the researcher obtaining information about an individual
that is sensitive and private without their permission. Alternatively, the researcher should ask
other subjects to pass along flyers, emails, information sheets, etc. that contain contact
information for the researcher to prevent a breach in confidentiality or an invasion of privacy.
In instances where the research subject is not sensitive (i.e., opinions on politics, consumer
opinions), a snowball recruitment method where one person provides the name and contact
information may be acceptable. If the topic is sensitive or personal, snowball sampling may be
justified, but care should be taken to ensure that the potential subjects’ privacy is not violated.
For example, studies of networks of drug users or studies tracking sex partners require extreme
caution with information gathered from one subject about another.
The steps taken to minimize the risk of violating an individual’s privacy should be articulated in
the recruitment section of the protocol. Current participants cannot receive incentives or
compensation for referrals.
One means of reducing the risks in snowball recruitment is for the researcher to ask subjects
whether they would be willing to pass some information about the study they just completed
to other potential subjects. The researcher may give the original subject an information sheet
or flyer that they can give to people they think might be interested and qualified. Then these
potential participants can contact the researcher if they are interested. The researcher must
provide the IRB with a copy of the recruitment item (which must include all of the same
