The sensitivity of the results was assessed with multiple additional analyses (see online supplement). For example, we considered the possible impact of incomplete or biased network data. If people who drink heavily are more likely to name people outside the study, underestimation of the effect of one person's alcohol consumption behavior on another might occur. Tests of the correlation between an individual's number of drinks per day and number of ties to people outside the study was not found to be significant (rho=0.01, p=0.15). This suggests that the network data generation procedure did not bias the analyses.
