Powell 1981

Methods	Setting: clinic, USA Recruitment: community volunteers Therapist: senior author
Participants	51 quitters (2 treatment dropouts excluded); 57% female, average age 36, average cigs/day 29
Interventions	All participants received the same cessation programme in a single group. Introductory meeting and 4 consecutive treatment meetings a week later, 1½ hours. Systematic focus on skill development. Also used a novel aversive smoking exercise conducted at each session Maintenance/relapse prevention conditions: 1. 4‐week support group (number of meetings not specified) 2. Telephone contact system allowing participants to phone each other 3. No contact control
Outcomes	Abstinence at 1 year, not defined Validation: none
Notes	Arm 2 not shown in graphs, all arms had similar quit rates
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	'Randomly assigned' with deviations for scheduling conflict and to separate families and friends
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Subjects randomly assigned to maintenance condition "at the end of the treatment phase", performance bias during treatment phase not likely
Blinding of outcome assessment (detection bias) All outcomes	High risk	No biochemical validation used, intensity of contact different between conditions with some in person, differential self‐report possible
Incomplete outcome data (attrition bias) All outcomes	Low risk	All but one participant contacted at follow‐up