Kenton 2007.

Study characteristics
Methods	Factorial RCT, individuals randomised
Data	Canada, community setting. All host trial participants in the intervention arm as a source of the retention trial sample. Total n = 281; age NR; sex NR.
Comparisons	Participants were randomised to: a) Receiving a monetary incentive alone (CAN$2 coin mailed with the questionnaire). b) Receiving a monetary incentive and 'high priority' stamp to the mailing envelope. c) Receiving lottery alone (draw for a CAN$50 gift certificate upon questionnaire receipt). Or a lottery and 'high priority' stamp to the mailing envelope.
Outcomes	Questionnaire return
Notes	Retention period: unclear
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Unclear	Not reported in the abstract.
Adequate sequence generation?	Unclear	Not reported in the abstract.
Blinding of participants and personnel?	Yes	Not reported in the abstract but unblinding not likely to impact objective outcome
Blinding of outcome assessment?	Yes	Not reported in the abstract. However, objective outcome, staff have no plausible additional opportunity to influence postal response rate once questionnaires sent.
Incomplete outcome data addressed? All outcomes	Unclear	Not reported in the abstract.
Free of selective outcome reporting?	Unclear	Not reported in the abstract.
Other sources of bias	Unclear	Abstract poorly reported.
Overall Risk of Bias	Unclear	Unclear