Guidelines: Snowballing - active and passive
Snowball recruitment - peer, network, or word-of-mouth recruiting - is acceptable only if it is in the passive form. That is, participants may be asked to discuss the research with friends/contacts that they think may be interested in volunteering to be participants. Those new participants can then be given information and the contact details of the research team so that they may independently volunteer to participate.
Active snowballing - when participants volunteer their friends/contacts or their friends’/contacts’ contact details directly to the research team - is generally not acceptable.