Year: 2025
Type: article
Abstract: Established in 2012, the Medicare Shared Savings Program (MSSP) is the centerpiece of Traditional Medicare's strategy to shift payment from fee-for-service to population-based payment. Medicare Shared Savings Program Accountable Care Organizations (ACOs) receive shared savings bonuses or losses based on whether they meet spending targets. The MSSP is voluntary, and ACOs and clinicians have considerable flexibility to enter and exit the program.1,2 The MSSP is considered the Centers for Medicare and Medicaid Services’ (CMS) most mature and largest value-based reform. However, this may mask underlying ACO or clinician attrition from the program, threatening the type of long-term practice transformation required to manage risk and coordinate care in new, challenging ways. In this context, we evaluated ACO and clinician trends in MSSP participation and attrition over time. We examined unadjusted trends in MSSP participation using CMS publicly reported data on MSSP ACOs from 2012 to 2024 and ACO Research Identifiable File data on clinicians from 2012 to 2021. Because ACO participation agreements were 3 years long for the majority of the study period (3 years from 2012 to 2019 and 5 years from July 2019 onward), we evaluated the probability of ACOs participating in the MSSP for at least 3, 6, and 9 years (ie, at least 1, 2, or 3 full participation cycles) among ACOs starting in or before 2022, 2019, and 2016, respectively. Clinicians included physicians, advanced practice providers (eg, nurse practitioners), and other clinicians such as occupational therapists. Because our clinician data ended in 2021 rather than 2024, we evaluated the probability of clinicians remaining in the program for at least 3, 6, and 9 years among clinicians starting in or before 2019, 2016, and 2013, respectively. Finally, we evaluated the probability of clinician exit from the MSSP among clinicians in ACOs that remained in the program. The total number of MSSP ACOs grew from 114 in 2012 to 548 in 2018 and then gradually fell to 480 in 2024 (Figure 1A). The number of MSSP beneficiaries grew from 2.1 M in 2012 to 10.1 M in 2018 and then plateaued, reaching 10.2 M in 2023 (data not shown). Across all cohorts, ACOs participated in the MSSP for an average of 5.3 years from 2012 through 2024. Figure 1B shows that 88%, 55%, and 35% of ACOs participated in the MSSP for at least 3 years (1+ cycles), 6 years (2+ cycles), and 9 years (3+ cycles), respectively. Participation and attrition in the MSSP. Panels (A)–(C): MSSP, Medicare Shared Savings Program; ACO, Accountable Care Organization. Accountable Care Organization participation was measured using ACO Public Use Files through 2024. Clinician participation was measured using ACO Research Identifiable File data through 2021. Because ACO data ended 3 years later than clinician data (2024 vs 2021), in Panel (B) we defined remaining in the MSSP for at least 3 years or 1 full participation cycle among cohorts starting in or before 2022 (ACOs) or 2019 (clinicians); at least 6 years or 2 participation cycles among cohorts starting in or before 2019 (ACOs) or 2016 (clinicians); or at least 9 years or 3 participation cycles among cohorts starting in or before 2016 (ACOs) or 2013 (clinicians). Clinician participation in the MSSP grew steadily from 39 k in 2012 to 656 k in 2021 but demonstrated significant attrition, with a 16% annual exit rate among clinicians in ACOs that remained in the program (Figure 1C). On average, clinicians participated in the MSSP for 3.6 years from 2012 through 2021, with 73%, 43%, and 23% of clinicians participating in the MSSP for at least 3 years (1+ cycles), 6 years (2+ cycles) and 9 years (3+ cycles), respectively (Figure 1B). Our study of the MSSP yielded 2 key findings. First, ACO and beneficiary MSSP participation stagnated from 2018 onward while overall clinician participation grew but with substantial attrition. Second, there were high rates of attrition by both ACOs and clinicians from the MSSP, with only about half of ACOs remaining in the MSSP for 6+ years or 2 contract cycles. A study limitation is not observing participation in other value-based reforms; it is possible some MSSP ACOs recently switched to ACO REACH or other models. Likewise, because some of the ACOs that leave the MSSP subsequently re-enter under a new ACO identification number, we only captured the ongoing participation of those ACOs that re-enter under the same ACO identification number. We also lack contemporary data on clinician participation in the MSSP. Stagnation and attrition may undermine the MSSP's central role in payment reform to Traditional Medicare. Although MSSP bonuses have grown over time and now outpace savings generated by ACOs,3 the high attrition by ACOs suggests that bonuses may be too small to entice ACOs to join or remain in the program, particularly after the MSSP shifted to include regional spending in ACO targets.1 ACOs may also struggle to recruit or retain clinicians in the face of growing competition from consolidating health systems, private equity, and Medicare Advantage.4 The recently introduced Value in Health Act seeks to increase clinician participation5 through enhanced MSSP incentives. Yet such reforms may further erode savings for CMS. A.A.M. and A.M.R.: study concept and design. P.L.G., A.A.M., and A.M.R.: acquisition, analysis, or interpretation of data, critical revision of the manuscript for important intellectual content, statistical analysis, and study supervision. A.A.M. and A.M.R.: drafting of the manuscript. P.L.G.: obtained funding. A.A.M. had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Supplementary material is available at Health Affairs Scholar online. P.L.G. was supported by the National Institute on Aging R01 AG053307-01. A.M.R. was supported by Arnold Ventures. The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation of the manuscript; or decision to submit the manuscript for publication.
Source: Health Affairs Scholar
Institutions: University of Michigan, Michigan Medicine, Brown University
Language: English
Subfield: Economics and Econometrics
Domain: Social Sciences
Open Access status: gold
Estimated APC paid: $3,150
OpenAlex ID: W4409069968