Peer effects in smoking cessation: An instrumental variables analysis of a worksite intervention in Thailand.

While smoking is widely acknowledged to be a social activity, limited evidence exists on the extent to which friends influence each other during worksite-based tobacco cessation interventions. Drawing on data from adult smokers (N = 1823) in a large, cluster randomized controlled trial in worksites in Thailand, this study examines the presence of social spillovers in the decision to abstain from smoking. We leverage a unique aspect of social network structure in these data-the existence of non-overlapping friendship networks-to address the challenge of isolating the effects of peers on smoking behavior from the confounding effects of endogenous friend selection and bidirectional peer influence. We find that individuals with workplace friends who have abstained from smoking during the trial are significantly more likely to abstain themselves. Instrumental variables estimates suggest that abstinence after 3 and 12 months increases 26 and 32 percentage points, respectively, for each additional workplace friend who abstains. These findings highlight the potential for workplace interventions to use existing social networks to magnify the effect of individual-level behavior change, particularly in low- and middle-income countries where tobacco cessation support tends to be limited.