Table 3.

Adjusted comparisons between internal and external patients for the numbers of laboratory tests, procedures, and medications ordered during the index visit

Outcomes	Independent variables†	Site A	Site B	Site C
	Best-fit model	Negative binomial, Exp (β‡)	Negative binomial, Exp (β‡)	Hurdle model
				n=0§	n>0
Laboratory tests	Internality (ref: external)	0.954*	0.990	0.643	0.860**
	Sex (ref: female)	1.092**	1.021	0.779	0.983
	Age	0.999	0.997*	1.008	0.997*
	Marriage (ref: single)	0.992	1.003	1.189	0.944*
	Race (ref: non-white)	1.029	1.089	0.664	1.152*
	Charlson comorbidity index	1.020**	1.011	0.861*	1.014*
	Hospitalized? (ref: no)	1.912**	1.236*	0.053**	1.373**

	Best-fit model	Negative binomial	Negative binomial	Negative binomial
Medications	Internality (ref: external)	0.664**	0.793	0.787*
	Sex (ref: female)	0.943	0.839*	1.038
	Age	0.998	0.987**	0.995*
	Marriage (ref: single)	1.022	0.957	0.853*
	Race (ref: non-white)	0.987	1.022	1.100
	Charlson comorbidity index	1.038**	0.992	1.029
	Hospitalized? (ref: no)	2.570**	2.155*	5.385**

	Best-fit model	Hurdle model		Hurdle model		Hurdle model
		n=0§	n>0	n=0§	n>0	n=0§	n>0
Procedures	Internality (ref: external)	0.874	0.957	1.354	0.829	1.015	0.901
	Sex (ref: female)	0.718	0.983	0.825	1.086	1.068	0.986
	Age	0.996	1.003	0.988	1.008*	1.001	1.001
	Marriage (ref: single)	1.057	0.999	1.301	1.010	1.218	0.958
	Race (ref: non-white)	0.878	0.957	1.104	1.122	0.656	1.104
	Charlson comorbidity index	1.025	1.008	0.988	0.977	0.990	0.995
	Hospitalized? (ref: no)	0.162**	1.377*	0.583	2.085*	0.194**	1.391**

*p<0.05, **p<0.001.

^†ref denotes the reference group to which another group is compared to determine changes in outcome.

^‡β: regression coefficients; Exp is the exponential function.

^§The odds ratio of having a count of zero.