Keding 2016.

Study characteristics
Methods	Factorial RCT, individuals randomised.
Data	UK, primary care setting. All host trial participants who consented to SMS notifications. Total n = 523; mean age 41.0 (SD 11.5) years; 76% females; 41% were full time workers.
Comparisons	Three sequential trials: Trial 1 (3‐month follow‐up): Intervention group received pre‐notification text. Control group received no text. Trial 2 (6‐month follow‐up): Intervention group received a pre‐notification text Control group received a post notification text Trial 3 (9‐month follow‐up): Intervention group received a post notification reminder text Control group did not receive a text
Outcomes	Proportion of participants who returned a valid questionnaire to the trial team.
Notes	Retention period: 3‐, 6‐ and 9‐months
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Unclear	Not reported in the paper.
Adequate sequence generation?	Unclear	Not reported in the paper.
Blinding of participants and personnel?	Yes	independent randomisation and that participants were blind to the trial hypothesis.
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	Yes	No concerns raised.
Free of selective outcome reporting?	Yes	No concerns raised.
Other sources of bias	Yes	No further concerns raised.
Overall Risk of Bias	Unclear	Unclear