Table 2.

Average values for all‐tracts diffusion measures and associations with age and study site

			Site effect		Age effect
	Mean	SD	t	P	r	P
Fractional Anisotropy	0.46	0.02	1.79	0.0757	−0.12	0.0069
Mean Diffusivity	0.84	0.03	4.59	<0.0001	0.24	<0.0001
Axial Diffusivity	1.30	0.03	4.99	<0.0001	0.24	<0.0001
Radial Diffusivity	0.61	0.03	2.98	0.0034	0.22	<0.0001

Site and Age effects are based on mixed model results that adjust for the correlated nature of twin data. Total N = 393.