Effect of the Affordable Care Act Medicaid Expansion on Emergency Department Visits: Evidence From State-Level Emergency Department Databases  Sayeh Nikpay, PHD, MPH, Seth Freedman, PHD, Helen Levy, PHD, Tom Buchmueller, PHD  Annals of Emergency Medicine  Volume 70, Issue 2, Pages 215-225.e6 (August 2017) DOI: 10.1016/j.annemergmed.2017.03.023 Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure 1 ED visits per capita by 2014 Medicaid expansion status. Source: AHRQ Fast Stats ED data. The figure plots mean seasonality-adjusted total ED visits per 1,000 state population in each calendar quarter, with 95% CIs. Data are weighted by 2014 state population. The solid line represents the best-fit line in the pre-expansion period (2012 Q1 to 2013 Q3), and the dashed line represents the projection of the best-fit line into the postperiod (2013 Q4 to 2014 Q4). Expansion states include Arizona, California, Hawaii, Iowa, Illinois, Kentucky, Maryland, Minnesota, North Dakota, New Jersey, Nevada, New York, Rhode Island, and Vermont, and nonexpansion states include Florida, Georgia, Indiana, Kansas, Missouri, North Carolina, Nebraska, South Carolina, South Dakota, Tennessee, and Wisconsin. Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure 2 ED payer mix by 2014 Medicaid expansion status. Source: AHRQ Fast Stats ED data. The figure plots the mean seasonality-adjusted share of all non-Medicare ED visits covered by Medicaid (A), with no source of coverage (B), and covered by private insurance (C), along with 95% CIs. Data are weighted by state population in 2014. The dashed vertical line represents the first quarter of the ACA’s Medicaid expansion, Q1. 2014 Expansion states include Arizona, California, Hawaii, Iowa, Illinois, Kentucky, Maryland, Minnesota, North Dakota, New Jersey, Nevada, New York, Rhode Island, and Vermont, and nonexpansion states include Florida, Georgia, Indiana, Kansas, Missouri, North Carolina, Nebraska, South Carolina, South Dakota, Tennessee, and Wisconsin. Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure 3 Relationship between changes in ED visits per capita and changes in Medicaid enrollment between 2013 and 2014. Source: AHRQ Fast Stats ED data. The y axis represents the change in total quarterly ED visits per 1,000 state population between 2013 and 2014, and the x axis represents the change in monthly Medicaid and Children's Health Insurance Program enrollment between 2013 and 2014. Each state is labeled with its postal abbreviation, and the best-fit line (5.75x–0.14) is plotted across expansion and nonexpansion states. Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure 4 Difference-in-differences estimates by ED visit type. Source: AHRQ Fast Stats ED data. The figure presents regression-adjusted difference-in-difference estimate and their 95% CI by ED visit type. Information on adjusted regression specification may be found in Appendix E2, available online at http://www.annemergmed.com. Expansion states include Arizona, California, Hawaii, Iowa, Illinois, Kentucky, Maryland, Minnesota, North Dakota, New Jersey, Nevada, New York, Rhode Island, and Vermont, and nonexpansion states include Florida, Georgia, Indiana, Kansas, Missouri, North Carolina, Nebraska, South Carolina, South Dakota, Tennessee, and Wisconsin. Total ED visits per capita are quarterly visits per 1,000 state population, and payer mix is the share of non-Medicare ED visits covered by Medicaid, with no source of coverage, and covered by private insurance. Standard errors are heteroscedasticity robust and clustered at the state level. Results are weighted by 2014 state population. The results are also robust to using a wild-cluster bootstrap to estimate P values corrected for a small number of clusters (see Appendix E2 and Table E3, available online at http://www.annemergmed.com). Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure E1 Medicare ED visits per capita by 2014 Medicaid expansion status. Source: AHRQ Fast Stats ED data. The figure plots mean seasonality-adjusted total Medicare ED visits per 1,000 state population in each calendar quarter, with 95% CIs. Data are weighted by 2014 state population. The solid line represents the best-fit line in the pre-expansion period (2012 Q1 to 2013 Q3) and the dashed line represents the projection of the best-fit line into the postperiod (2013 Q4 to 2014 Q4). Expansion states include Arizona, California, Hawaii, Iowa, Illinois, Kentucky, Maryland, Minnesota, North Dakota, New Jersey, Nevada, New York, Rhode Island, and Vermont, and non-expansion states include Florida, Georgia, Indiana, Kansas, Missouri, North Carolina, Nebraska, South Carolina, South Dakota, Tennessee, and Wisconsin. Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure E2 ED visits per capita by state. Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions

Figure E3 ED payer mix by state. Annals of Emergency Medicine 2017 70, 215-225.e6DOI: (10.1016/j.annemergmed.2017.03.023) Copyright © 2017 American College of Emergency Physicians Terms and Conditions