In this model, the fixed effects (D, A) are latent variables that summarize the net effect of all nonobserved fixed factors that exert a constant effect on the measures of MD and AAD, respectively, over time. These factors include all childhood, family, and personal characteristics that have a fixed effect on outcomes over time; thus, they may include both genetic and environmental influences. The time-dynamic components of the model (Ut, Wt) represent the effect of all other sources of variance in MD and AAD, respectively, that are not solely due to fixed factors. The equations defining this model were as follows. For the model equations: Dt = D + Ut (t = 1, 2, 3); At = A + Wt (t = 1, 2, 3); U3 = B1W3 + B3U2 + ν3; W3 = B2U3 + B5W2 + τ3; U2 = B1W2 + B4U1 + ν2; and W2 = B2U2 + B6W1 + τ2. For the model assumptions: cov(D, Ut) = cov(D, Wt) = cov(A, Ut) = cov(A, Wt) = 0 (t = 1, 2, 3); cov(D, νt) = cov(D, τt) = cov(A, νt) = cov(A, τt) = 0 (t = 2, 3); cov(νt, τs) = cov(νt, νs) = cov(τt, τs) = 0 for t ≠ s (t, s = 2, 3); cov(Dt, νs) = cov(Dt, τs) = cov(At, νs) = cov(At, τs) = 0 for t < s; and cov(Ut, νs) = cov(Ut, τs) = cov(Wt, νs) = cov(Wt, τs) = 0 for t < s. In these equations, the terms νt and τt (t = 2, 3) represent disturbance terms reflecting unexplained sources of variation in the time-dynamic components of MD symptoms (Ut) and AAD symptoms (Wt), respectively. The coefficients B1 and B2 represent the reciprocal effects of AAD on MD symptoms and vice versa, respectively, within each period. The coefficients B3 and B4 represent the across-time stabilities in the time-dynamic components of MD symptoms, and the coefficients B5 and B6 represent the across-time stabilities in the time-dynamic components of AAD symptoms.