Figure 1.

Parameter estimates from the best-fit multivariate twin model applied to the DSM-IV criteria for alcohol dependence. Three genetic and two individual-specific environmental common factors were identified, as well as individual-specific environmental factors unique to each criterion. The strongest genetic loading on each criterion is highlighted in blue. E for individual-specific environmental effects. Subscript numbers refer to common factors (for example, E₁ refers to the first individual-specific environmental common factor), whereas subscript numbers following the letter ‘S’ (for specific) refers to criteria-specific factors (for example, E_S1 refers to the individual environmental effects specific to the first criterion). Squares are observed variables and circles/ovals are latent variables.