Greig 2017.

Study characteristics
Methods	Parallel RCT, individuals randomised
Data	UK, secondary care. All host trial participants were included in this trial. Total n = 60; mean age 5.8 (SD 3.5); 48.3% females.
Comparisons	Intervention group 1 had a postal follow‐up. Intervention group 2 had a clinic follow‐up.
Outcomes	Participants with a valid response.
Notes	Retention period: 4 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	Not clear if participants were blinded to effect of embedded trial intervention on retention but unblinding not a likely 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	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