The portion of the variability in each substance that was not explained by SDV could be decomposed into substance-specific genetic and/or environmental effects. In males, while the point estimates from the full model indicated that there was evidence for substance-specific genetic and non-shared environmental effects on alcohol, tobacco, and cannabis, the best-fitting model indicated additive genetic and non-shared environmental effects on alcohol and tobacco, and only non-shared environmental effects on cannabis. In females, the best-fitting Common Pathway model confirmed the pattern of effects observed in full model (i.e., shared and non-shared effects on alcohol and tobacco, and additive genetic and non-shared environmental effects on cannabis). Thus, differences in the magnitude of genetic and environmental effects in males and females that were apparent in the univariate model appear to arise from substance-specific mechanisms.
