Tai 1997.

Study characteristics
Methods	Parallel RCT, individuals randomised
Data	UK, primary care setting. All host trial participants lost to follow‐up who had a telephone. Total n = 148, median age 43.7; sex NR
Comparisons	Intervention group 1 received a telephone reminder after non‐response to 1st reminder. Intervention group 2 were sent a new set of questionnaires with the reminder letter and sent after non‐response to 1st reminder.
Outcomes	Questionnaires returned
Notes	Retention period: unclear
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Unclear	Not reported in the paper.
Adequate sequence generation?	Unclear	Just says randomised
Blinding of participants and personnel?	Unclear	Does not mention blinding and it is not clear if the researchers making calls were also part of the main trial team. In principle, they could have influenced the outcome depending on their knowledge of allocation.
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	Unclear	No further concerns raised.
Overall Risk of Bias	Unclear	Unclear