Fig. 2.

Simplified diagram of the structural equation model for the general fractional anisotropy (FA) variable. FA in white matter tracts 1–12 was measured at baseline (age 73) and follow-up (age 76), and a General FA factor extracted at each wave. From these a latent change score variable (Δ General FA) was calculated. Then, each of the predictor variables was assessed for its relation with baseline level (path A) and change (path B). The equivalent model for general mean diffusivity used only 11 tracts. The equivalent models for grey matter volume, white matter volume, and white matter hyperintensity volume did not use latent factors at each wave