Parents' and older siblings' smoking during childhood: changing influences on smoking acquisition and escalation over the course of adolescence.

This study investigated prospectively the change in the influence of parents' and older siblings' smoking at the start of the childhood and adolescent smoking acquisition period (i.e., 3rd grade, or age 8) on the initiation and escalation of smoking over the course of adolescence. In a sample of 5,520 individuals in 3rd grade, we measured parents' and older siblings' smoking. Individuals' smoking data were provided at four grade intervals over the course of adolescence. The influence of parents' smoking, measured at 3rd grade, was stable and significant for the transition to trying smoking and increased over the course of adolescence for the transition from monthly to daily smoking (p = .001). In contrast, we found no evidence that influence of older siblings' smoking, measured at 3rd grade, changed (p>.05) across the grade intervals for any adolescent smoking transition. The results suggest that the influence of parents' smoking on smoking initiation is stable and enduring whereas it increases substantially for smoking escalation occurring over the course of adolescence.