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Acad Emerg Med. 2013 Oct;20(10):1026-32. doi: 10.1111/acem.12236.

When coverage expands: children's health insurance program as a natural experiment in use of health care services.

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Department of Emergency Medicine, University of Michigan, Ann Arbor, MI; Robert Wood Johnson Foundation Clinical Scholars Program, University of Michigan, Ann Arbor, MI.



Expanding insurance coverage is designed to improve access to primary care and reduce use of emergency department (ED) services. Whether expanding coverage achieves this is of paramount importance as the United States prepares for the Affordable Care Act.


Emergency and outpatient department use was examined after the State Children's Health Insurance Program (CHIP) coverage expansion, focusing on adolescents (a major target group for CHIP) versus young adults (not targeted). The hypothesis was that coverage would increase use of outpatient services, and ED use would decrease.


Using the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS), the years 1992-1996 were analyzed as baseline and then compared to use patterns in 1999-2009, after the CHIP launch. Primary outcomes were population-adjusted annual visits to ED versus nonemergency outpatient settings. Interrupted time series were performed on use rates to ED and outpatient departments between adolescents (11 to 18 years old) and young adults (19 to 29 years old) in the pre-CHIP and CHIP periods. Outpatient-to-ED ratios were calculated and compared across time periods. A stratified analysis by payer and sex was also performed.


The mean number of outpatient adolescent visits increased by 299 visits per 1,000 persons (95% confidence interval [CI] = 140 to 457), while there was no statistically significant increase in young adult outpatient visits across time periods. There was no statistically significant change in the mean number of adolescent ED visits across time periods, while young adult ED use increased by 48 visits per 1,000 persons (95% CI = 24 to 73). The adolescent outpatient-to-ED ratio increased by 1.0 (95% CI = 0.49 to 1.6), while the young adults ratio decreased by 0.53 across time periods (95% CI = -0.90 to -0.16).


Since CHIP, adolescent non-ED outpatient visits have increased, while ED visits have remained unchanged. In comparison to young adults, expanding insurance coverage to adolescents improved use of health care services and suggests a shift to non-ED settings. Expanding insurance through the Affordable Care Act of 2010 will likely increase use of outpatient services, but may not decrease ED volumes.

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