Logistic regression analyses were used to test the significance of the association between substance use and educational attainment within individuals while controlling for the non-independence of twin pairs, as shown in Table 3. The first column of Table 3 confirms that, in the general population, each substance use measure was associated with reduced educational attainment, even after controlling for covariates. The remaining columns of Table 3 display results from tests examining whether the three “at risk” groups (individuals in pairs concordant for substance risk behavior, the substance using twin from discordant pairs, and the non substance using twin from discordant pairs) had significantly lower educational attainment relative to individuals in pairs concordant for low substance risk (the comparison group). In unadjusted models, individuals in all three “at risk” groups had significantly lower educational attainment for almost all substance use measures than did individuals in pairs concordant for low substance risk (the sole exception was a lack of association between alcohol dependence and educational attainment in low risk twins from discordant twin pairs). We observed little change in point estimates after
