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Purpose

The purpose of this guideline is to:

• Provide clear guidance on the use of snowball recruitment and its considerations for proper implementation within a study design.

Background

Snowball recruitment is an interconnected approach to recruiting potential participants into a research study. This technique relies on leveraging existing networks to expand outreach and attract more participants. Unlike traditional recruitment efforts, snowball recruitment uses referrals and word of mouth.

Method 1: Snowball Recruitment: Potential Participants Contacted by Existing Participants (Not by Researcher)

This form of snowball sampling is the most common method employed by researchers and involves asking current participants to mention the study to people whom they think might be interested in participating (i.e., referrals). Researchers can assist by providing current participants with a short description of the study and their contact information via posters/flyers that can be sent out to the new participant through the participant they have recruited.

Interested referrals can contact the researcher directly. A consideration in having current participants provide referrals’ name or contact information directly to the researcher is the possible feeling of violation of the referrals’ privacy. For example, if participants were to be recruited based on sensitive criteria, such as an illness, asking current participants to refer others may reveal confidential information about these people and leave the potential participant feeling uneasy or not comfortable with the researcher contacting them, without any warning. This can be avoided by having current participants mention the study directly to referrals, who can then contact the researcher if interested.

NOTE: that recruiting in this manner may raise other ethical issues. For example, if current participants have some degree of power over referrals, such as an employer-employee relationship, then asking current participants to mention the research to others may raise issues of undue influence.

Researchers are encouraged to think through the ethical issues that are relevant to their specific situation and to explain, in their application, how their chosen option handles these issues.

If this type of snowball recruitment is used, researchers must include the materials and/or instructions (e.g., recruitment script and researcher contact information) that they will be providing to participants within their ethics application.

Method 2: Snowball Recruitment: Researcher Contacts Potential Participant

This form of snowball sampling involves asking current participants to provide the names and contact information of referrals so that researchers can contact them directly. Typically, this is the more useful option for researchers. However, it can be problematic when the recruitment criteria involve sensitive information, possibly breaching referrals’ privacy, or when referrals are likely to be sensitive about being contacted directly (e.g., police, military, etc.). In such cases, current participants need to obtain referrals’ permission to provide their contact information to researchers.

At a minimum, researchers must indicate where they obtained referrals’ contact information from (consistent with any recruitment that involves contacting participants directly) when contacting referrals. This means revealing the participant’s identity to those whose names they provide. The participants must consent to this (e.g., it must be described in the LOI and a check box to indicate “yes, you may reveal my identity to those participants I have referred”). In certain situations, there may be ethical reasons not to reveal this information. Researchers need to justify this in their application. If this type of snowball recruitment is used, the researcher needs to include the recruitment script for such referrals in the ethics application.

Important Considerations

• Current participants cannot receive any compensation for providing referrals or be offered any incentives to provide referrals.
• Current participants must not be required to refer others or incur any penalty for not referring other participants.