Starr 2015.

Study characteristics
Methods	2×2 partial factorial RCT, individuals randomised.
Data	UK, secondary care setting. Participants who were newly randomly assigned to the host trial had not reached the 4‐week time point and were willing to supply a mobile phone number, or an e‐mail address were included. Total n = 418; mean age 41 (SD 11.1) years; 20% females.
Comparisons	Two trials were included in this study: Trial 1: Intervention group received an SMS text message pre‐notification of the delivery of the initial 4‐ and 12‐week questionnaires. Control group received no message. Trial 2 (for participants who did not respond to the initial 4‐ or 12‐week questionnaire): Intervention group received an e‐mail which included a link to complete the questionnaire online or was invited to return the paper copy if they wished. Control group received their reminder by post with a further copy of the questionnaire.
Outcomes	Questionnaire return.
Notes	Retention period: 1‐ or 3‐ months questionnaire
Risk of bias
Item	Authors' judgement	Support for judgement
Allocation concealment?	Yes	A computer‐generated system that was concealed and remote from the users.
Adequate sequence generation?	Yes	Participants were randomly allocated to the intervention on a 1:1 basis,
Blinding of participants and personnel?	Yes	Due to the nature of the intervention, it was not possible to blind the participants or trial office staff to allocation. Unblinding not likely to impact objective outcome.
Blinding of outcome assessment?	Yes	The researchers remained blinded.
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	Yes	Low