The present study has a number of strengths, including representative sampling of twin-families and assessment of voluntary sexual onset through young adulthood. However, findings should be considered in light of limitations beyond aforementioned reduced statistical power. With respect to measurement, we used lifetime history of parental alcoholism as age of onset was not available by coparent or twin report. Although previous research supports temporal primacy of parental alcoholism relative to separation in the current sample [16], if parents no longer meet diagnostic criteria, risk to offspring of chronically dependent parents will be underestimated. In addition, mechanisms underlying observed associations, at least in European ancestry families, were not examined. Lax or inconsistent monitoring and presence of a stepparent are each predictive of early sex [9] and are also more prevalent in separated families compared to families where parents remain together [38]. Deviant peer association may also play a role (e.g., [39,40]). Examination of potential mediators including parenting and peer influences will be an important focus of future studies. Lastly, analyses were limited to female twins and their families and may be of reduced generalizability without extension to male and non-twin samples.
