To examine whether a general vulnerability exists for substance consumption at each assessment wave, common and independent pathway models were fit to the three substances within each wave, separately in males and females (excluding members of opposite-sex pairs). Both models assume that a common factor influences the observed variables but differ in the way the common factor(s) influence the variables. In the independent pathway model, the common genetic and environmental factors influence the observed variables directly, with separate genetic and environmental components estimated for each of the variable residuals.
