Table 2.

List of clinical and imaging covariates that are associated with changes in total cortical volume [24]. Models #2 and #4 in Table 1 control for these covariates. The definition for each covariate includes its type and range

Variable	Type	Range
Age	Continuous	23 yo–67 yo
Ethnicity	Nominal	See Table 3
Gender	Binary	See Table 3
Log-cerebral vault	Continuous	13.5–14.3
Scanner (# of scanners at site)	Nominal	Univ Wash (1 scanner) Univ Texas (1 scanner) Hopkins (1 scanner) New York (2 scanners) UCSD (2 scanners)
D-drug* ever	Nominal	1 = current 2 = past 3 = never
Inhalant abuse ever	Binary	Yes or no
Methamphetamine abuse ever	Binary	Yes or no
Global deficit score	Continuous	0–3.47

^*D-drug = dideoxynucleoside reverse transcriptase inhibitors.