When new participants are recruited by current participants to become part of a study sample, it is called “snowball sampling.” This is a non-probability sampling technique that can be a practical way to identify and recruit individuals with certain characteristics to a research study who might otherwise be challenging to find (e.g., individuals with a rare disease who are part of a Facebook support group may invite other members to participate in a survey, etc.).  Note: this type of sampling is at higher risk of sampling bias.

Referral incentives can be a useful recruiting tool. But is it ethical to place an advertisement online or at a research center that states “Refer a friend to our study and receive a $50 gift card.”?

The short answer (as always) is, ‘it depends’.

Who can receive these payments?

Regulations (21 CFR 56 and 45 CFR 46) are silent with respect to the use of compensation or incentives in research, whether given to researchers or study participants. Pearl IRB does not allow payment of referral fees to medical professionals or research staff. However, incentives to study participants may be appropriate in certain circumstances.

FDA states that “Paying research subjects in exchange for their participation is a common and, in general, acceptable practice”, and notes that IRBs “should review both the amount of payment and the proposed method and timing of disbursement to assure that neither are coercive or present undue influence.” Likewise, federal regulations (21 CFR 50.20, 45 CFR 46.116) require that IRBs determine that informed consent “minimize[s] the possibility of coercion or undue influence”, but do not define either of these terms.

However, the Belmont Report states that: “Coercion occurs when an overt or implicit threat of harm is intentionally presented by one person to another in order to obtain compliance…Undue influence, …, often occurs through an offer of an excessive or inappropriate reward or other overture in order to obtain compliance…undue influence also can be subtle…Because of their relative nature and lack of clear-cut standards … investigators and IRBs must be vigilant.

So, what issues must investigators and IRBs consider before initiating this type of recruitment policy? For example, there could be a concern that participants might, so that they would collect the referral payment, engage in threatening behaviors (i.e., coerce) to force their enrollment in the study and/or put significant pressure on (i.e., influence unduly) their acquaintances.

Study protocols must acknowledge these potential issues exist and provide methods to prevent these behaviors from occurring. There are practical methods that can be put in place to minimize the chance of undue influence or coercion occurring. The IRB will assess each protocol to ensure incentives, and how they will be provided, are clearly described. For example, concerning referral fees: the IRB will review the planned structure of the referral program and suggest updates so that coercion and undue influence are minimized. Restrictions might include limiting the amount of the payment, the number of referrals an individual may make, or not having the referral payment dependent on the enrollment of the referred individuals.

Lastly, the consent process should reduce the likelihood of coercion or undue influence happening. Referred individuals should understand that the choice to participate is, as always, voluntary, and that the individual making the referral will not be advised of the referred person’s participation and will not be a part of their consent or research process.