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Snowball sampling is a recruitment technique in which research participants are asked to assist researchers in identifying other potential subjects. 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. The method that minimizes risk would be the preferred choice. 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.1
If the topic of the research is not sensitive or personal, it may be acceptable for subjects to provide researchers with names and contact information for people who might be interested in participation. 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.
Acceptable alternatives that reach the same potential subjects include:
• The study team member may provide information to subjects and encourage them to pass it on to others who may be interested or eligible. The information provided to enrolled subjects (fliers, letters of explanation, etc.) must be approved by the IRB. Interested prospective participants could then contact the project for more info and possible inclusion.
• The study team member may ask subjects to obtain permission from others prior to disclosing their contact information. In this scenario, the researcher would not directly contact the referred/potential subject without permission from the potential subject and would not have access to any information about a potential subject without permission from that individual.
1. Examples provided by the National Science Foundation, http://www.nsf.gov/bfa/dias/policy/hsfaqs.jsp#snow
Guidance Version Date: September 14, 2010