predictive of respondent behavior (55). The questionnaire for PSI preceded the interview for RSI - we consider this to be a strength of our study – twins reported objectively on PSI as adolescents and at a later time point, when they were past the period of risk for initiation of alcohol, cigarettes and cannabis, were interviewed about their own substance use. Third, we excluded 199 African-American women from the present analyses – variation in patterns of RSI may be attributable to ethnic differences – for instance, when African-American subjects were included, factor loadings for PSI were markedly different (for e.g. the loading for smoking cigarettes regularly dropped from 0.74 to 0.42 with generally lower loadings for licit substances) suggesting differences in the factorial structure. While it would be important to study the effects of PSI on RSI in African-American women, the small sample size precluded us from formally testing these differences.
