A principal strength of the present work is the use of the twin-offspring design which permits a sensitive test for measured environmental influences while accounting for genetic vulnerability due to parental ND. Additional strengths include the large sample size and non-clinical sample that enhance generalizability while avoiding bias inherent to clinical samples. The structured method of data collection reduces interviewer bias. Last the large age range of the offspring permitted modeling the major smoking milestones in adolescents and young adults. We computed post-hoc sensitivity analysis using data only on offspring 18 years and older and can conclude that point estimates were not significantly different before and after limiting the cohort to these older aged offspring.
