Dorman 1997.

Study characteristics
Methods	Parallel RCT, individuals randomised.
Data	UK, secondary care setting. Multinational host trial. Only UK sites took part in this trial. Participants who had been entered by UK centres who were not known to be dead. Total n = 2253, age NR, sex NR.
Comparisons	Intervention group 1 received a short questionnaire: EuroQol questionnaire (six separate questions and a visual analogue scale) sent by post. Intervention group 2 received a long questionnaire: SF­36 (34 separate questions) sent by post.
Outcomes	Questionnaire response rate
Notes	Retention period: unclear. Follow‐up time point not specified. Authors mention as quote:"response to first mailing or response after two mailings".
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Unclear	Not discussed in the paper.
Adequate sequence generation?	Yes	Authors response "generated by a computer".
Blinding of participants and personnel?	Yes	Authors reported, quote: "there was no blinding for either study staff or participants." Unblinding not likely to impact objective outcome.
Blinding of outcome assessment?	Yes	Authors reported, quote: "there was no blinding for either study staff or participants". No clarification on outcome assessment. However, objective outcome, participants blind (did not know there was a study) staff had no plausible additional opportunity to influence postal response rate once questionnaires sent.
Incomplete outcome data addressed? All outcomes	Yes	Everyone is included in the denominator as well as a compilation of data
Free of selective outcome reporting?	Yes	All defined outcomes reported
Other sources of bias	Yes	No further concerns raised.
Overall Risk of Bias	Unclear	Unclear