Accountable care organizations (ACOs) in the Medicare Shared Savings Program (MSSP) are associated with modest savings. However, prior research may overstate this effect if high-cost clinicians exit ACOs.
To evaluate the effect of the MSSP on spending and quality while accounting for clinicians' nonrandom exit.
Similar to prior MSSP analyses, this study compared MSSP ACO participants versus control beneficiaries using adjusted longitudinal models that accounted for secular trends, market factors, and beneficiary characteristics. To further account for selection effects, the share of nearby clinicians in the MSSP was used as an instrumental variable. Hip fracture served as a falsification outcome. The authors also tested for compositional changes among MSSP participants.
Fee-for-service Medicare, 2008 through 2014.
A 20% sample (97 204 192 beneficiary-quarters).
Total spending, 4 quality indicators, and hospitalization for hip fracture.
In adjusted longitudinal models, the MSSP was associated with spending reductions (change, −$118 [95% CI, −$151 to −$85] per beneficiary-quarter) and improvements in all 4 quality indicators. In instrumental variable models, the MSSP was not associated with spending (change, $5 [CI, −$51 to $62] per beneficiary-quarter) or quality. In falsification tests, the MSSP was associated with hip fracture in the adjusted model (−0.24 hospitalizations for hip fracture [CI, −0.32 to −0.16 hospitalizations] per 1000 beneficiary-quarters) but not in the instrumental variable model (0.05 hospitalizations [CI, −0.10 to 0.20 hospitalizations] per 1000 beneficiary-quarters). Compositional changes were driven by high-cost clinicians exiting ACOs: High-cost clinicians (99th percentile) had a 30.4% chance of exiting the MSSP, compared with a 13.8% chance among median-cost clinicians (50th percentile).
The study used an observational design and administrative data.
After adjustment for clinicians' nonrandom exit, the MSSP was not associated with improvements in spending or quality. Selection effects—including exit of high-cost clinicians—may drive estimates of savings in the MSSP.
Primary Funding Source:
Horowitz Foundation for Social Policy, Agency for Healthcare Research and Quality, and National Institute on Aging.
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Author, Article, and Disclosure Information
University of Michigan Medical School and School of Public Health, Ann Arbor, Michigan (A.A.M.)
University of Michigan Medical School and Institute for Healthcare Policy and Innovation, Ann Arbor, Michigan (J.M.H.)
University of Michigan Medical School, School of Public Health, Gerald R. Ford School of Public Policy, and Institute for Healthcare Policy and Innovation, Ann Arbor, Michigan (J.Z.A.)
University of Michigan School of Public Health, and Institute for Healthcare Policy and Innovation, Ann Arbor, Michigan, and National Bureau of Economic Research, Cambridge, Massachusetts (E.C.N.)
University of Michigan Medical School, Ann Arbor, Michigan (P.L.Y.)
University of Michigan School of Public Health, Center for Evaluating Health Reform, Institute for Healthcare Policy and Innovation, Ann Arbor, Michigan (A.M.R.)
Note: Dr. Ryan had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Financial Support: Mr. Markovitz is supported by the Horowitz Foundation for Social Policy and by grant R36HS025615 from the Agency for Healthcare Research and Quality. Dr. Hollingsworth is supported by grants R01HS024728 and 1R01HS024525-01A1 from the Agency for Healthcare Research and Quality. Dr. Ryan is supported by grant R01AG047932 from the National Institute on Aging.
Disclosures: Dr. Hollingsworth reports other support from University of California, San Francisco, that had no effect on the analysis presented in this manuscript. Authors not named here have disclosed no conflicts of interest. Disclosures can also be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M18-2539.
Editors' Disclosures: Christine Laine, MD, MPH, Editor in Chief, reports that her spouse has stock options/holdings with Targeted Diagnostics and Therapeutics. Darren B. Taichman, MD, PhD, Executive Editor, reports that he has no financial relationships or interests to disclose. Cynthia D. Mulrow, MD, MSc, Senior Deputy Editor, reports that she has no relationships or interests to disclose. Jaya K. Rao, MD, MHS, Deputy Editor, reports that she has stock holdings/options in Eli Lilly and Pfizer. Catharine B. Stack, PhD, MS, Deputy Editor, Statistics, reports that she has stock holdings in Pfizer, Johnson & Johnson, and Colgate-Palmolive. Christina C. Wee, MD, MPH, Deputy Editor, reports employment with Beth Israel Deaconess Medical Center. Sankey V. Williams, MD, Deputy Editor, reports that he has no financial relationships or interests to disclose. Yu-Xiao Yang, MD, MSCE, Deputy Editor, reports that he has no financial relationships or interest to disclose.
Corresponding Author: Andrew M. Ryan, PhD, Department of Health Management and Policy, University of Michigan School of Public Health, M3124 SPH II, 1415 Washington Heights, Ann Arbor, MI 48109-2029; e-mail, [email protected]
Current Author Addresses: Mr. Markovitz: UM Institute for Health Policy and Innovation, Center for Evaluating Health Reform, North Campus Research Complex, 2800 Plymouth Road, Building 16, 016-100N-28, Ann Arbor, MI 48109.
Dr. Hollingsworth: University of Michigan Medical School, Urology, North Campus Research Complex, 2800 Plymouth Road, Building 16, 016-112W, Ann Arbor, MI 48109-2800.
Dr. Ayanian: University of Michigan Medical School, UM Institute for Health Policy and Innovation, North Campus Research Complex, 2800 Plymouth Road, Building 16, 440E, Ann Arbor, MI 48109-2800.
Dr. Norton: University of Michigan School of Public Health, M3108 SPH II, 1415 Washington Heights, Ann Arbor, MI 48109-2029.
Ms. Yan: University of Michigan Medical School, Urology, North Campus Research Complex, 2800 Plymouth Road, Building 16, 016-100S-14, Ann Arbor, MI 48109-2800.
Dr. Ryan: University of Michigan School of Public Health, M3124 SPH II, 1415 Washington Heights, Ann Arbor, MI 48109-2029.
Author Contributions: Conception and design: A.A. Markovitz, J.M. Hollingsworth, J.Z. Ayanian, E.C. Norton, A.M. Ryan.
Analysis and interpretation of the data: A.A. Markovitz, J.M. Hollingsworth, J.Z. Ayanian, E.C. Norton, A.M. Ryan.
Drafting of the article: A.A. Markovitz.
Critical revision of the article for important intellectual content: A.A. Markovitz, J.M. Hollingsworth, J.Z. Ayanian, A.M. Ryan.
Final approval of the article: A.A. Markovitz, J.M. Hollingsworth, J.Z. Ayanian, E.C. Norton, P.L. Yan, A.M. Ryan.
Statistical expertise: A.A. Markovitz, E.C. Norton, A.M. Ryan.
Obtaining of funding: A.A. Markovitz, J.M. Hollingsworth.
Administrative, technical, or logistic support: A.M. Ryan.
Collection and assembly of data: J.M. Hollingsworth, P.L. Yan.
This article was published at Annals.org on 18 June 2019.