Table 4.

Predictors of caffeine intake in adult smokers with and without serious mental illness, using multivariate gamma regression with log link

	B	SE	Wald Chi-Square	p	Effect Size^a
Adults with schizophrenia, bipolar disorder, and healthy controls, analysis of serum caffeine (n=213)
Age	.014	.006	5.385	.020	1.410
Race/Ethnicity
White	Ref	-	-	-
Black	−.637	.166	14.762	<.001	−47.112
Hispanic/Latino	−.320	.211	3.300	.129
Not Listed	−.481	.335	2.060	.151
Sex
Male	Ref	-	-	-
Female	.154	.137	1.26	.262
Diagnosis Group
No Psych Dignoses	Ref	-	-	-
Schizophrenia	.500	.173	3.381	.004	64.872
Bipolar Disorder	.502	.156	10.306	.001	65.202
Cigarettes per day	.009	.008	5.384	.238
Global Hepatic Inducer Use
No	Ref	-	-	-
Yes	.700	.439	2.542	.111
3HC Ratio	−.309	.189	2.678	.102
Adults with schizophrenia, bipolar disorder, and healthy controls, analysis of self-report caffeine intake (n=228)
Age	.015	.006	7.293	.007
Race/Ethnicity
White	Ref	-	-	-
Black	−.233	.147	2.527	.112
Hispanic/Latino	.029	.216	.018	.893
Not Listed	−.300	.319	.888	.346
Sex
Male	Ref	-	-	-
Female	−.024	.130	.033	.856
Diagnosis Group
No Psych Dignoses	Ref	-	-	-
Schizophrenia	.050	.161	.095	.758
Bipolar Disorder	.359	.154	5.440	.020	43.190
Cigarettes per day	.013	.008	2.548	.007	1.308
Global Hepatic Inducer Use
No	Ref	-	-	-
Yes	.057	.448	.016	.899
3HC Ratio	.018	.202	.008	.929

The effect size is derived using the following formula: (exp(B)-1) x 100 and is intepretted as the percent change in the outcome for every one unit change in the predictor, or in the case of categorical variables, the percent change in outcome compared to the reference group.