Table 2.

Topics for data extraction and associated measures.

Topics		Measures
Study setting (context)
	Country	Country
	Target population	Target population (specify)
	Purpose	Study purpose (eg, population estimates, social networks, intervention)
Seed recruitment and selection (implementation characteristics)
	Seed recruitment	Recruitment platform (specify)
	Seed selection	Selection procedure (specify)
	Number of seeds recruited	Number of seeds recruited that participated in the study
Peer recruitment (mechanisms of impact)
	Incentives	Material or nonmaterial (specify) Single or double (specify) Maximum value of incentive
	Recruitment options	Recruitment options (specify)
	Coupons	Number of coupons allowed (ie, that a participant can forward)
	Reminders	Reminders sent to enhance recruitment (yes/no)
Recruitment performance (outcomes)
	Total participants recruited	Sample sizea
	Successfully recruiting participantsb,c	Proportion of seeds who successfully initiated recruitment Proportion of all participants who successfully recruited peers to the study
	Waves	Maximum number of waves observed
	Equilibrium	Equilibrium reached (yes/no, and after how many waves)
	Duration of data collection	Duration of data collection
	Barriers and facilitators	Barriers and facilitators indicated to have influenced recruitment performance

^aSample size was calculated as sample size minus duplicate or fraudulent entries, if reported.

^bWe defined a successfully recruiting participant as a participant who invites at least one other person who participates in the study, regardless of the eligibility (the latter says more about how strict or elaborate researchers set eligibility criteria rather than about participants’ ability to peer recruit). This excludes participants who merely sent out invitations with no response. If reported, duplicate or fraudulent entries were excluded.

^cIf not otherwise reported, this metric was manually counted and calculated from the reported recruitment tree.