Table 2.

Trends* in selected markers of acuity or complexity for ED visits

	2006	2009	2012	Time trend per year, % (95% CI)	P value
Hospital admission rate	40.1%	38.7%	35.9%	−0.68 (−0.71 to −0.65)	<0.001
ICU admission rate	11.7%	12.6%	12.3%	+0.11 (0.09 to 0.12)	<0.001

Mean number of services per admission†	2006	2009	2012	Change in services per year, % (95% CI)	P value
All admissions	1.28	1.31	1.41	+0.02 (0.018 to 0.021)	<0.001
Low intensity	1.22	1.25	1.37	+0.02 (0.017 to 0.025)	<0.001
High intensity	1.30	1.31	1.41	+0.017 (0.015 to 0.019)	<0.001

Mean number of services per outpatient‡ ED visit	2006	2009	2012	Change in services per year, % (95% CI)	P value
All outpatient visits	7.11	8.05	8.60	+0.25 (0.25 to 0.26)	<0.001
Low intensity outpatient visits	5.28	5.39	5.22	−0.008 (-0.01 to −0.003)	0.001
High-intensity outpatient visits	12.85	13.37	13.68	+0.14 (0.13 to 0.15)	<0.001

*Inpatient services are ICD-9 procedures.

†Outpatient services are represented using Current Procedural Terminology/Healthcare Common Procedure Coding System codes.

‡Longitudinal linear regression models were used to estimate the time trend, adjusting for patient age, race, sex and Medicaid eligibility. The yearly estimates were based on binomial regression for hospital and ICU admission rates and negative binomial regression for mean number of services per admission/outpatient visit and used generalised estimating equations to account for clustering at the level of the ED.

ED, emergency department; ICD-9, International Classification of Diseases, Ninth Revision; ICU, intensive care unit.