It is not possible to measure all environmental influences on offspring. We lacked data on offspring perception of peer smoking and lacked self reported measures from siblings on smoking, alcohol and drug use. Expansion of the shared environment assessment may reveal key parent, sibling and peer level variables that have not been adequately measured. Longitudinal data will help clarify the direction of effect for peer substance use. Follow-up is necessary to collect more detailed assessment of the parent-offspring environment, to expand upon sibling substance use and drug problems and the impact of older as compared to younger siblings on offspring smoking and to model trajectories related to life events associated with adulthood.
