Blyth 2015

Methods	Setting: participants' own homes, UK Recruitment: short‐term quitters recruited from NHS Stop Smoking Clinics
Participants	1404 ex‐smokers (4‐week abstinence), 702 in intervention group and 702 in control 47.3% male, average age 47, average cigarettes per day 20
Interventions	1. Relapse prevention: eight 'Forever Free' self‐help booklets by post 2. Control: single leaflet 'Learning to Stay Stopped' routinely given to NHS patients
Outcomes	Continuous abstinence from 2 to 12 months Validation: CO < 10 ppm at 12 months
Notes	Funding: "This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme" Declaration of Interest: "Paul Aveyard has done ad hoc consultancy and research for the pharmaceutical industry on smoking cessation."
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Simple randomisation method used
Allocation concealment (selection bias)	Unclear risk	Quote: "The participant allocation was ‘concealed’ because the recruitment of quitters occurred before the random allocation." However, it was unclear how this would achieve allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Blinding not performed, but face‐to‐face contact was the same between the two groups, so performance bias unlikely.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Biochemically validated abstinence
Incomplete outcome data (attrition bias) All outcomes	Low risk	Follow‐up rates similar in both groups (intervention = 87%, control = 85%)