Table 8.

Summary of the results from ‘ retention ’ studies included in the review (n = 26 studies)

Barriers	Strategies
Difficulty maintaining contact; highly mobile populations; frequently changing contact numbers	• Implementing tracking procedures with multiple contact methods – i.e., phone, mail, email [17,20,22,30,39,40,54,66],[74,75,81,85].
	• Contact details of significant others [20,30,76,66].
Practical barriers such as transport difficulties, lack of child care, lack of leave from work	• Incentives (cash and other gifts) to study participants as reimbursement for time [18,22,23]*,[24]*,[30,39,40,70-73,76,80,81,123].
	• Participant-centred approach: personalised, tailored individualised approach to follow-up calls or visits [39,54,66,73,96,123] and flexible (accommodating) protocols [16,30,35,66,70,72,74,76] and providing transport or child care [30].
	• Scheduling follow-up assessments to coincide with existing appointments [22,30].
	• Toll-free numbers [39,54].
Forgetting to return for follow-up	• Use of study logos on gifts [74].
	• Phone text message reminders [65].
	• Keep in regular contact [18,22,30,65,67,76,81,118].
	• Highlighting benefits of research during follow-up contact [30,40,71,72].

*Indicates good evidence from randomised controlled trial (see also Table 1).