Figure 1.

Path diagram representing the Cholesky decomposition of the twin data. The model consists of three additive genetic (A1-3) and three unique environmental (E1-3) factors, with each successive factor loading on fewer variables. In Figure 1A, A3 and E3 represent insomnia-specific factors. In Figure 1B, the phenotypes are presented in reverse order and A3 and E3 are depression-specific effects. Common environmental factors (C) have been omitted because they were not statistically significant in any models. Coefficients are shown for all statistically significant paths. Note that, regardless of order of entry for the phenotypes, the best fitting model included only a single genetic factor.