Assessing the Impact of Parity in the Large Group Employer-Sponsored Insurance Market: Final Report



This study assessed the impact of the Paul Wellstone and Pete Domenici Mental Health Parity and Addiction Equity Act of 2008 (MHPAEA) on the private, large group employer-sponsored insurance market. The impact of MHPAEA on mental health (MH) and substance use disorder (SUD) utilization and spending outcomes was assessed using interrupted time series regression analysis, focusing on outpatient services. In lieu of a control group, we compared MH and SUD services with non-behavioral health services. MHPAEA had significant and positive effects on any use of SUD services and the frequency of SUD services used. Increases in insurer and enrollee spending on SUD outpatient services were driven by increased utilization, and not enrollee cost sharing. When examined separately, similar effects were found for both opioid use disorder (OUD) and non-OUD SUD services, supporting the conclusion that effects can be attributed to parity and not to general trends related to the OUD crisis. Although MHPAEA had similar positive impacts on utilization of and spending on MH outpatient services, these effects were more moderate. MHPAEA led to a dramatic shift toward out-of-network spending for SUD outpatient services. In secondary analyses, we examined the impact of parity on three subgroups: individuals with serious mental illness, those with OUD, and high utilizers of behavioral health services. The effects on use and spending outcomes in these secondary analyses were consistent with overall findings. Sensitivity analyses were conducted by including only continuously contributing employers, which produced very similar results. Finally, the analyses provide evidence that the effects of parity on outpatient services were continuing up until the study end date of September 30, 2015, particularly for SUD services. [111 PDF pages]

This report was prepared under contract #HHSP223201600023I between the U.S. Department of Health and Human Services (HHS), Office of Disability, Aging and Long-Term Care Policy (DALTCP) and Truven Health Analytics. For additional information about this subject, you can visit the DALTCP home page at or contact the ASPE Project Officers, Laurel Fuller and D.E.B. Potter, at HHS/ASPE/DALTCP, Room 424E, H.H. Humphrey Building, 200 Independence Avenue, S.W., Washington, D.C. 20201;

DISCLAIMER: The opinions and views expressed in this report are those of the authors. They do not reflect the views of the Department of Health and Human Services, the contractor or any other funding organization. This report was completed and submitted on November 30, 2017.


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