Lung Health Study.

Methods	Setting: 10 study centres, USA Recruitment: Healthy smokers with mild airway obstruction, not required to be interested in quitting
Participants	5887 smokers; 37% F, av. age 48, av. cpd 31 Providers: specialist counsellors
Interventions	1. Advice from study physician with stress on high risk of COPD, 12 group sessions over 10 weeks, beginning on quit day, initially 4 sessions/week, 2 mg nicotine gum available for 6 months, maintenance and recycling sessions offered long term. Cessation intervention participants also randomized to bronchodilator or placebo arms, pooled here. 2. Usual Care, no intervention
Outcomes	Abstinence at 1 year (PP) (also assessed annually for 5 years, data not used here) Validation: CO at each visit, cotinine at 1y
Notes	Numbers quit at 1y estimated from graph. At 5y sustained abstinence rates reported to be approximately 22% vs 5%
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomized, computer generated separately for each centre, blocks of random permutations of varied length (Reported in Connett 1993)
Allocation concealment (selection bias)	Low risk	Centralised verification of eligibility & allocation
Incomplete outcome data (attrition bias) All outcomes	Low risk	˜95% follow‐up at 1y. Non attenders counted as smokers