Table 4.

Effect of incentives

Study ID	Study design	Comparator	Intervention	Difference in response rate (primary end point)	Difference in response rate (secondary end point)
Brealey 2007 [35]	Historical control study design	No incentive (the first 105 patients did not receive the £5 incentive)	The subsequent 442 patients received unconditional direct payment of £5 for the completion and return of questionnaires	The response rate (12 months after randomisation) following reminders for the historical controls was 78.1% (82 of 105) compared with 88.0% (389 of 442) for those patients who received the £5 payment (diff = 9.9%, 95% CI 2.3 to 19.1%).	No secondary end point reported
Rodgers 2016 [36]	Prospective cohort study	In-person cash incentive for the first 111 participants	The subsequent 358 participants were given reloadable bank card for incentive payments	Retention rates among the card-paid participants at 6 months was 80% vs. 68% cash-paid	Retention rates among the card-paid participants at 12 months was 72% vs. 66% cash-paid