Measures of Outcome
All 893 subjects were included in analyses of the primary outcome. The primary outcome variable was the point-prevalence rate of abstinence at 6 and 12 months of follow-up. Subjects were considered to be abstinent if they reported not smoking since the preceding clinic visit and had an expired carbon monoxide concentration of 10 ppm or less. Subjects were considered to be continuously abstinent if they had not smoked after the quitting day, as confirmed by a carbon monoxide concentration of 10 ppm or less at all clinic visits during the 12-month study. Secondary outcome measures included withdrawal symptoms, body weight, and Beck Depression Inventory scores.