Table 3.

Individual and unique contributions to g from global MRI measures across middle and older age groups.

Model	Middle (≤ 63.29 yrs)				Older (> 63.29 yrs)
	Individual		Simultaneous		Individual		Simultaneous
	Std. Est.	p	Std. Est.	p	Std. Est.	p	Std. Est.	p
TBV	0.287	<0.001	–	–	0.308	<0.001	–	–
R2	0.082		–	–	0.095		–	–
GM	0.276a	<0.001	0.159	<0.001	0.328a	<0.001	0.298	<0.001
NAWM	0.257	<0.001	0.134	<0.001	0.268	<0.001	0.054	<0.001
WMH	−0.115a	<0.001	−0.092	<0.001	−0.165a	<0.001	−0.132	0.007
gFA	0.113	<0.001	0.051	0.029	0.108	<0.001	−0.096	<0.001
gMD	−0.065		0.012	0.628	−0.126		−0.131	<0.001
R2			0.054				0.136

Note. Std. Est: standardised estimate. Groups split at 63.29 years. ^aMagnitudes were significantly different by age, according to a χ² test (FDR q < 0.05). Models are corrected for sex; brain measures also corrected for head positioning confounds. Associations between g and TBV were not significantly different between middle and older ages: Δχ²(1) = 3.874, p = .049, ΔAIC = 2, ΔsaBIC = −3.223. However, the magnitude of g associations with multiple global measures (simultaneously modelled) were significantly different between age groups: Δχ²(7) = 183.22, p ≤.001, ΔAIC = 169, ΔsaBIC = 134. TBV: total brain volume, GM: grey matter volume, WM: white matter volume, WMH: white matter hyperintensity volume, FA: fractional anisotropy, MD: mean diffusivity.