and those that are individual-specific, with more robust evidence for the shared influences being correlated than the non-shared (Young et al., 2006). However, a study using a subset of the data from this study showed that in African American (AA) women, the relationship between timing of onset of cigarette smoking and cannabis use was prominently attributable to overlapping individual-specific environmental factors (r = 0.95) (Sartor et al., 2009).
