The results of this study should be interpreted in the context of several limitations. First, our assessment of parent monitoring was based on self report, as elicited with multi-item questions, which is less comprehensive than multi-informant assessments from both parents and children (37). Second, the retrospective nature of this study’s ascertainment of childhood environmental risk exposures is subject to recall bias, which may have affected the validity and reliability of reported parent monitoring. However, this concern is reduced somewhat given that our main effects association of parent monitoring with nicotine dependence is consistent with longitudinal work among adolescents (24). Third, our measure of parent monitoring is one of various instruments assessing parent monitoring, and does not differentiate different aspects of parenting practices such as parent involvement and parent discipline (24, 38). Fourth, we also have to be cautious in labeling parent monitoring solely as an environmental risk, as parent monitoring itself may be influenced by both genetic and environmental factors, reflecting both genetically-influenced characteristics of the parents (39–42), though neither genetic variant examined here was correlated with parent monitoring (r=0.03,
