Lewis 2017.

Study characteristics
Methods	RCT, individuals randomised.
Data	UK, primary care setting. All host trial participants, as a source of the retention trial sample. Participants who were due to be sent a follow‐up questionnaire for the host trial were included. Total n = 611; mean age 74.0 (SD 6.5) years; 59.5% female.
Comparisons	Intervention group received a questionnaire with a printed Post‐it® note. Control group questionnaires without a note.
Outcomes	Questionnaire return
Notes	Retention period: 4 months.
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Yes	The personnel who added the Post‐it® notes to questionnaires were different to those who had participant contact to ensure allocation concealment.
Adequate sequence generation?	Yes	Participant allocation was carried out by simple computerised randomisation using an SQL function through the trial management database by the York Trials Unit.
Blinding of participants and personnel?	Yes	Not reported in the paper but unblinding not likely to impact objective outcome
Blinding of outcome assessment?	Yes	Not reported in the paper.However, objective outcome, staff have no plausible additional opportunity to influence postal response rate once questionnaires sent.
Incomplete outcome data addressed? All outcomes	Unclear	Participants who reached four months follow‐up before commencement recruitment, as well as participants who asked to be withdrawn from the CASPER trials or did not want to receive a questionnaire at this time point were excluded.
Free of selective outcome reporting?	Yes	No concerns raised.
Other sources of bias	Yes	No further concerns raised.
Overall Risk of Bias	Unclear	Unclear