Table 4.

Covariate analysis

Phenotype#		Covariate	Effect&	p-value
Aversive effects
Respiratory depression (CO2)		Age	+ 0.43mmHg per decade	0.015
		Gender	+ 1.39mmHg men versus women	0.008
Respiratory depression (RR)		-	-	-
Trail making test (s)		Age	+ 4.0% per decade	<0.001
		Education	+ 9.2% high school versus college	0.001
Sedation (VAS)		Mood	− 0.2 VAS per unit (POMS)	0.023
Nausea	– average (VAS)	-	-	-
	– maximum (VAS)	-	-	-
Pruritus	– average (VAS)	Age	− 4.1 VAS units per decade	<0.001
		Gender	− 8.3 VAS units men versus women	0.018
		Depression	+ 8.7 VAS units per category (BDI)	0.007
	– maximum (VAS)	Age	− 6.4 VAS units per decade	<0.001
		Gender	− 10.5 VAS units men versus women	0.028
		Depression	+ 13.0 VAS units per category (BDI)	0.001
Dizziness	– average (VAS)	Gender	− 14.8 VAS units in men versus women	<0.001
		Race	+ 16.1 VAS units in Asian versus others	0.002
	– maximum (VAS)	Gender	− 16.5 VAS units in men versus women	<0.001
		Race	+ 19.4 VAS units in Asian versus others	0.002
		Depression	+ 11.6 VAS units per category (BDI)	0.007
Reinforcing effects
Drug liking	– average (VAS)	Race	+ 16.4 VAS units Caucasian versus others	0.006
		Mood	+ 0.6 VAS units per unit (POMS)	0.001
	– maximum (VAS)	Ethnicity	− 15.1 VAS units Hispanics versus non-Hispanics	0.048
		Race	+ 28.1 VAS units Caucasian versus others	<0.001
		Mood	+ 0.4 VAS units per unit (POMS)	0.013
Drug disliking	– maximum (VAS)	Age	+ 5.1 VAS units per decade	0.010

^# CO2 = carbon dioxide, RR = respiratory rate, s=seconds, VAS = visual analogue scale (0–100);

^&BDI: Beck Depression Inventory (no, mild, moderate, severe depression); POMS: profile of mood states subscale for anxiety; (range 0–36); Race: African American, American Indian, Asian, Caucasian and Pacific Islander;