Fig 1. A path diagram of the cross-lagged model shown for one twin.

Latent factors appear in circles (i.e., A for genetic factors, C for shared environments, E for nonshared environments), while observed (measured) variables appear in rectangles. Latent factors at age 3 represent residual variances. Standardized path estimates for the latent factors are indicated by lowercase letters (e.g., a₁, c₁, e₁). Cross-age stability is represented by b₁₁ and b₂₂, while b₁₂ and b₂₁ indicate cross-lagged effects. Double-headed arrows linking two latent factors represent genetic, shared environmental, or nonshared environmental correlations (i.e., r_g1, r_c1, r_e1, r_g2, r_c2, r_e2).