McColl 2003 ‐ Trial 1.

Study characteristics
Methods	RCT, clusters randomised
Data	UK. Primary care setting. All host trial participants, as a source of the retention trial sample. Total n = 6576; mean age 59.6 (SD 13.7) years, 50.8% females; 66% were married; 60% were unemployed; 54.2% had no formal education qualifications.
Comparisons	Participants were randomised to two different versions of a self‐response questionnaire: Intervention group 1, condition‐specific measures of quality of life preceded generic instruments Intervention group 2, the relative position of the questionnaire was reversed.
Outcomes	Response rates on the questionnaire
Notes	Retention period: 9 months
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Unclear	Not described only that participants were randomly assigned to each group.
Adequate sequence generation?	No	A random sample of 80 participants per condition per practice was selected.
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	Not reported in the paper.
Free of selective outcome reporting?	Unclear	Not reported in the paper.
Other sources of bias	Yes	No further concerns raised.
Overall Risk of Bias	No	High