Once GRSs were computed for each individual, we examined whether the GRS was associated with frequency of cigarettes smoked per day. Next, we examined the relationship between aspects of the individual's social environment, including the experience of traumatic life events, neighborhood social cohesion and neighborhood physical disorder, and whether each environmental variable was associated with the number of cigarettes smoked per day in this population. Because of the skewed distribution of cigarettes smoked per day, all analyses were conducted using Poisson regression in SAS (SAS Institute, 2003), adjusting for sex, age and ancestral components (described previously), as well as appropriate sample weights.
