May 2006.

Methods	Randomised controlled trial Study dates:1999‐2000 Group treatment programme at smoker's clinic; random assignment by group
Participants	564 smokers, 38% male, mean age 43.6 yrs; mean number of cigarettes smoked per day 23 Partner: smoker attending same cessation group
Interventions	(1) Control condition: 6 weekly 1 to 1½ hour group sessions (n = 326, 20 groups) (2) Buddy condition: Buddy system was used (choosing someone in a group to be a buddy). Buddy intervention occurred during final 20 minutes of 2nd session (n = 238, 14 groups)
Outcomes	Self‐reports, CO test at weeks 0, 1, 4, 26.
Notes	NRT or bupropion was not withheld. 4 buddy groups and 2 solo groups used NRT or bupropion. Funding source: not reported Author declarations: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Participants were "assigned consecutive numbers and each number was randomised by computer random number generation to the ‘buddy’ or ‘solo’ condition".
Allocation concealment (selection bias)	Low risk	Quote: "Researchers were not aware of the group allocation until recruitment for that group was complete and all respondents were allocated to the next available group so selection would not occur".
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Abstinence was verified using exhaled CO.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	All dropouts counted as smokers, but number of participants lost to follow‐up not provided