2025 ACO Publications

2025 | 2024 | 2023 | 2022 | 2021 | 2020

ACO Research Summary

Do Medicare Accountable Care Organizations Impact Health Care Utilization Among Long-Stay Nursing Home Residents?
Date: April 2025
Source: Journal of the American Medical Directors Association
This study assessed the impact of Medicare Shared Savings Program (MSSP) ACOs on health care utilization among long-stay nursing home (NH) residents included 158,259 fee-for-service Medicare beneficiaries who were long-stay NH residents in 2011 or 2018. In each year, residents were included in the sample the first time their Minimum Data Set (MDS) assessments ( index MDS) met the following inclusion criteria: (1) aged 66+; (2) dependence in two or more activities of daily living; (3) neither enrolled in hospice nor in coma; and (4) NH length of stay ≥90 days. Researchers followed residents’ health care utilization and Medicare expenditures for 1 year after their index MDS date. Outcomes included any health care utilization in different care settings (i.e., inpatient, outpatient emergency room visit/observational stay, skilled nursing facility, hospice) and corresponding Medicare expenditures. Researchers used difference-in-differences models to estimate the association between ACO attribution and health care utilization in 2018, using 2011 as the pre-ACO baseline. To determine ACO attribution among the 2011 cohort, we developed an algorithm to replicate the ACO attribution in 2018 and used it to identify residents who would have been attributed to 2018 ACOs back in 2011. To address the endogeneity issue between ACO attribution and utilization outcomes, the study used an “intention-to-treat” design to determine ACO attribution. Adjusted difference-in-differences results showed a lack of significant associations between ACO attribution and health care utilization or Medicare expenditures among long-stay NH residents.

Organizational Characteristics Associated with Sustained Participation in Internal Quality Improvement: Findings from Two Waves of a National Sample of Physician Practices in the United States
Date: March 2025
Source: Social Science & Medicine
This study examined whether organizational innovation characteristics, including organizational culture, health information technology (HIT) capacity, and ACO affiliation distinguish physician practices that sustain their engagement in internal quality improvement (Q)I from those that do not. Researchers linked two waves of the National Survey of Healthcare Organizations and Systems (NSHOS) fielded between 2017-2018 and 2022–2023 among physician practices in the United States to assess organizational characteristics associated with sustained engagement in QI (n = 714 practices). The study found that higher innovative culture scores were associated with almost three times the odds of sustained QI. Although high HIT capacity was also associated with greater odds of sustained versus non-sustained QI across both survey waves, this finding was not statistically significant. Similarly, the study did not find statistically significant association between ACO affiliation (whether commercial, Medicare, or Medicaid) and sustained internal QI. Although ACO affiliation may signal willingness to participate in QI as a means to advance evidence- and value-based care and HIT capacity may facilitate improvement activities, these characteristics may not assure sustained internal QI engagement without an organizational culture aligned with QI. Policies that advance organizational capacity to develop a learning-oriented innovative culture could enable sustained QI engagement at the physician practice level.

The Evolution of Medicare: Challenges, Responses, and Prospects 
Date: February 28, 2025
Source: Journal of Health Politics, Policy and Law
Over Medicare’s 60-year history, the program has evolved to cover a greater share of the population and pay for an increasing share of the nation’s health care bills. As Medicare has grown, so have its challenges. The traditional Medicare program has failed to keep pace with a rapidly changing health care sector and demographic shifts. Constrained by its own benefit design, Medicare has allowed privately contracted health plans (Medigap, Medicare Advantage) to provide much needed yet inadequate remedies to the program’s shortcomings. After briefly recounting Medicare’s origins, this article discusses how Medicare’s founding statutes have hindered its ability to respond to new and growing challenges along the dimensions of cost-sharing, cost containment, and benefit design. The authors then propose a three-pronged approach to reforming Medicare’s benefit structure, including a simplified enrollment process, a single benefit that brings together the program’s constituent parts (Part A, Part B, and Part D), and a new organizational structure for care delivery based on the program’s experience with ACOs.

The Challenge of Medicare and Medicaid Integration for Dual Eligible Individuals Under 65
Date: February 24, 2025
Source: Health Affairs Forefront
This article discusses the opportunity for ACOs in traditional Medicare to improve and integrate care for the dual-eligible population younger than 65 as an alternative to Medicare Advantage (MA). Given the heterogeneity of the dual-eligible population younger than age 65, a one-size-fits-all approach may not be as effective as a whole-person approach that considers health and social needs. To date, 12 percent of dual eligibles in traditional Medicare are aligned to an ACO. ACOs could provide more integration through better care coordination and potentially offer social benefits, such as meals, transportation, or help with utility bills and rent for dual-eligible individuals covered under traditional Medicare, including those younger than age 65. However, more research is needed to consider opportunities for integration of care through ACOs for dual-eligible individuals, including those younger than age 65.

Evolution of Clinical Health Information Exchanges to Population Health Resources: A Case Study of the Indiana Network for Patient Care
Date: February 24, 2025
Source: BMC Medical Informatics and Decision Making
This case study examines the potential role of health information exchanges (HIEs) in expanding population health management by describing the evolution of the Indiana Network for Patient Care (INPC) and discussing examples of its innovations that support both population health and clinical applications. Although INPC data are primarily gathered from and used in health care settings, their use for population health management and research has increased. The INPC supports participating in ACOs by providing more complete and comprehensive clinical data than an individual ACO can typically obtain on its own. This information includes healthcare encounters and specific data such as medications, laboratory test results and procedures. For ACOs in Indiana, INPC information supports coordinating care, reducing the duplication of services, and calculating quality metrics. INPC data provided to ACOs vary depending on the organization and its needs as well as its capabilities. For larger organizations, completely automated information transfers are common, such as ADT alerts or CCD transmissions. The receiving organizations typically ingest this information into their health IT infrastructure, such as electronic data warehouses. The ACOs then route information directly to individuals who need it or process it further, such as through population health management and analytics systems. Smaller organizations with less sophisticated health IT infrastructures often receive information from the INPC in spreadsheets and similar formats. The HIE also provides reports and dashboards for population health management directly. 

Spending Changes After Moving to Areas with Greater ACO Participation Among Nonattributed Medicare Beneficiaries
Date: February 20, 2025
Source: JAMA Network Open
This study estimated spending changes by non-ACO–attributed Medicare beneficiaries after they moved to geographic areas with greater ACO participation. This repeated cross-sectional study analyzed claims from a 20% representative sample of all Medicare beneficiaries, aged 65 to 99 years, from 2009 to 2017. The sample consisted of Medicare beneficiaries who were never attributed to an ACO and moved once across hospital service areas during the study period (movers) and was supplemented by a 20% random sample of beneficiaries who never moved (nonmovers). The study of 62,618 mover and 433,298 nonmover Medicare beneficiaries found that non-ACO–attributed beneficiaries’ move to areas with more Medicare beneficiaries in ACOs was associated with reduced outpatient facility spending and increased physician services spending. The changes in spending on acute inpatient or total acute care were minimal. These findings suggest that although no substantial spillovers from ACOs to nonattributed beneficiaries occurred, outpatient care may shift away from higher-cost facility settings in markets with greater ACO penetration.

Impact of Medicare Accountable Care Organizations on Surgical and Postoperative Expenditures Among Patients with Gastrointestinal Cancer
Date: February 14, 2025
Source: Surgery
This study examined whether Medicare Shared Savings Program ACO participation was associated with lower surgical and postoperative care spending related to gastrointestinal cancer surgery. Individuals who underwent gastrointestinal cancer surgery between 2016 and 2020 were identified from the Medicare database. Difference-in-differences analysis was used to evaluate risk-adjusted 30-day and 1-year hospital level cost savings before and after ACO participation. A total of 23,357 Medicare beneficiaries underwent gastrointestinal cancer surgery (pancreas: n = 2,747; 11.8%; liver: n = 877, 3.8%; biliary tract: n = 1,168, 5%; colon: n = 15,845, 67.8%; rectum: n = 2,720, 11.6%) at 57 ACO-participating hospitals and 171 nonparticipating hospitals. Median patient age was 75 years with roughly one-half of patients being female (n = 12,207, 52.3%). Of note, participation in the ACO was not associated with reductions in total Medicare payments for 30-day surgical episodes or for 1-year episodes. These trends were similar for other health care services including inpatient care, outpatient care, home health assistance, and skilled nursing facilities.

Changes in U.S. Primary Care Access and Capabilities During the COVID-19 Pandemic
Date: February 7, 2025
Source: JAMA Health Forum
This study examined changes in primary care access and capabilities during the COVID-19 pandemic. The analysis included two rounds of survey responses, 2017-18 and 2022-23, from 710 practices, of which 234 were independently owned, 105 were physician group owned, and 321 were hospital/health system owned in 2017 to 2018.  Sixty-eight practices reported no ACO participation, 107 joined between surveys, and 486 otherwise participated in ACOs. Access to care (measured as extended weekday or weekend hours) was reported to decline from the first survey in 2017-18 to the second in 2022-23. Hospital/health system practices and ACO participants had higher rates of extended weekday hours than their comparators in 2022 to 2023. Average capability scores increased from 51 to 54 (increase of 4 points). There was wide variation in scores within all ownership and ACO participant or nonparticipant groups. Capability scores were higher on average for more integrated practices (for physician groups compared to independent practices and for ACO participants compared to nonparticipants.

‘On the OB Side of Things, It’s Completely Disconnected’: Early Implementation of Medicaid Accountable Care Organizations and Health Care in the Perinatal Period
Date: February 1, 2025
Source: Women’s Health Issues
This study examined how individuals in ACO leadership have approached program design to address maternal health and how these programs have shaped health care utilization and maternal health from the perspective of postpartum ACO beneficiaries and clinicians. Researchers conducted virtual semi-structured interviews with three key stakeholder groups in Massachusetts (ACO leaders, maternity care clinicians, and Medicaid ACO members who had given birth within the past 6–24 months) between November 2021 and May 2023. Thirty-three interviews were conducted: four with ACO leaders, 15 with maternity care clinicians, and 14 with ACO members. Maternity care clinicians did not perceive that ACO implementation had substantially impacted perinatal health care. Interviews with ACO leadership suggested that the lack of perceived impact may be partially explained by competing priorities; the Massachusetts Medicaid ACOs generally did not focus on maternal health during the initial implementation period. Postpartum ACO members were largely unaware of ACOs. Lack of explicit attention to the perinatal population in Medicaid financing and delivery system reforms may reduce the potential impact in improving outcomes.

Accountable Care Organizations, Child Opportunity Index, and Complicated Appendicitis in Children
Date: February 2025
Source: Journal of Surgical Research
This study examined the impact of ACO enrollment on the association of low scores on the Child Opportunity Index (COI) with the likelihood of a child having complicated appendicitis. Using a single-institution, retrospective review of children with public insurance undergoing appendectomy for acute appendicitis, COI and clinical confounders were compared by simple versus complicated appendicitis. Among 1,337 children, 31.0% had complicated appendicitis. Most (78.6%) were enrolled in the ACO; this was not different between simple and complicated appendicitis. As overall COI quintile decreased (lower opportunity), the percentage of children with complicated appendicitis increased. The association between COI and complicated appendicitis was not modified by ACO enrollment. COI and ACO enrollment were not associated with postoperative complications, except children in the ACO had fewer 30-day readmissions (4.2% versus 14.6%, P < 0.001) compared to those with other public insurance.

Future Of Accountable Care: Lessons Learned and Potential Paths Forward During A Time Of Transition
Date: January 31, 2025
Source: Health Affairs Forefront
Accountable care is not at the top of the news, and, historically, the shift to paying for value has had bipartisan support, including across the prior Trump and Biden administrations. But accountable care itself is at an inflection point, more prevalent than ever but still an “alternative” to fee-for-service. Trump administration priorities related to preventing chronic disease complications and reducing federal spending could provide tailwinds for accountable care, but policy disruptions and uncertainty could create headwinds as well. This article examines the landscape during the transition when opportunities are emerging but by no means resolved.

The Spillover Effect of the CMS Innovation Center
Date: January 21, 2025
Source: NEJM Catalyst
The models established by the CMS Innovation Center to reduce Medicare and Medicaid spending while maintaining or enhancing the quality of care—such as Bundled Payments for Care Improvement and Comprehensive Primary Care—affect the overall health care delivery system beyond participating organizations. This study, based on interviews with providers, payers, management services organizations, and industry and academic experts, examined the drivers of spillover effects from the CMS Innovation Center’s programs.

Improving CMS Financial Benchmarking: Lessons Learned by The Innovation Center
Date: January 16, 2025
Source: Health Affairs Forefront
The CMS Innovation Center uses financial benchmarks as one of several mechanisms to incentivize model participants to reduce health care spending and establish performance thresholds. Financial benchmarks for model participants estimate the expected cost of included health care items and services for attributed individuals during a fixed performance period. CMS calculates financial benchmarks using expenditures from CMS claims data and frequently incorporates three elements: how much CMS has historically paid for the related health care item(s) and service(s), how payments might change, and the characteristics and health of the patients served by the model. The Innovation Center uses financial benchmarks in many models, for example, in the Accountable Care Organization Realizing Equity, Access, and Community Health (ACO REACH) Model, the Kidney Care Choices Model, and the newly announced Transforming Episode Accountability Model (TEAM) and States Advancing All-Payer Health Equity Approaches and Development (AHEAD) models. The Innovation Center is committed to an ongoing cycle of designing, refining, and testing new benchmarking methodologies, particularly as we learn from ongoing model tests. This article lays out the four principles and key considerations the Innovation Center uses when setting financial benchmarks for upcoming models.

Medicare Accountable Care Organizations In 2023: Large Savings With Increasing Value-Based Programmatic Competition
Date: January 15, 2025
Source: Health Affairs Forefront
In late October 2024, CMS released data for the 11^th year of the ACO Medicare Shared Savings Program (MSSP), marking the seventh consecutive year that the MSSP has achieved savings for Medicare (based on comparisons to the administrative benchmark) and the largest savings in the program’s history. The number of participating ACOs decreased slightly from 2022 due to a confluence of factors, but as fewer beneficiaries enroll in traditional Medicare and alternative programs for ACOs such as the ACO Realizing Equity, Access, and Community Health (ACO REACH) Model, attribution in shared savings programs (SSPs) will be challenging. As always, comparisons against benchmarks, including quality, should be interpreted with caution given that savings are calculated from benchmarks set in advance based on a blend of historical and regional spending, the results are unadjusted, and more ACOs are claiming uncontrollable circumstance adjustments (often a function of natural disasters and other emergencies).

Key findings include:

• Non-dually enrolled beneficiaries presented higher risk scores and greater average net savings per capita compared to the dually enrolled population.
• Overall, 453 different organizations participated in the MSSP, a 6 percent decline from the previous year’s 482 participants. The total number of beneficiaries also declined by roughly 2 percent from 2022 to 2023.
• For the second year since the MSSP began, the majority of ACOs took downside risk: 67 percent of ACOs were two-sided risk, while 33 percent were upside only. ACOs in two-sided risk were nearly twice as likely to achieve shared savings than upside-only ACOs.
• In 2023, the ACOs in the MSSP produced more than $2.10 billion in net savings and generated $3.08 billion in savings compared to benchmarks, or $234 net savings per capita, a 22 percent increase in net savings per capita and almost double the net savings compared to benchmarks from 2022.
• Consistent with last year’s findings, ACOs with a larger share of participating primary care physicians were more likely to receive shared savings and higher net savings per capita.
• Non-dually enrolled beneficiaries presented higher risk scores and greater average net savings per capita compared to the dually enrolled population.

How Benchmark Changes Affect Participation in Accountable Care Organizations: Prospects for Voluntary Payment Models
Date: January 2025
Source: American Journal of Health Economics
In voluntary alternative payment models, participation is essential for model viability and the progression of provider payment reform. This study examines participation decisions of ACOs in the Medicare Shared Savings Program. Researchers leveraged a natural experiment in which a 2017 rule change introduced differential shocks to an ACO’s baseline spending and performance-year spending. The net effect was an effective change in benchmarks that varied across ACOs. Dropout was 7 percentage points more likely among ACOs with effective benchmark decreases. While small reductions in the effective benchmark did not affect program participation, larger reductions increased dropout by 11 percentage points. ACOs with spending already above their benchmarks were particularly sensitive to effective benchmark reductions, consistent with the program’s weak long-term incentives to reduce spending. The results highlight the causal role benchmarks play in determining ACO participation and the need to consider the consequences of participation effects in the design of new payment models.

High-Intensity Home-Based Rehabilitation in a Medicare Accountable Care Organization
Date: January 8, 2025
Source: The American Journal of Managed Care
Patients are often discharged to a skilled nursing facility (SNF) for postacute rehabilitation. Functional outcomes achieved in SNFs are variable, and costs are high. Especially for ACOs, home-based postacute rehabilitation offers a high-value option if outcomes are not compromised. This study compared outcomes for episodes in a novel high-intensity home-based rehabilitation (HIHR) model vs a SNF. Medicare patients from a large integrated multihospital health system who had low to moderate medical complexity and mild to moderate mobility deficits at hospital discharge were included. The primary exposure was discharge to HIHR (intervention) or a SNF (control) after hospitalization. The primary outcome was Activity Measure for Post-Acute Care (AM-PAC) mobility score. Secondary outcomes were Medicare costs within 30 and 90 days post hospitalization, 30-day readmission rate, and index hospital length of stay (LOS). 

There were 171 patients discharged to HIHR and 841 to SNFs. The adjusted AM-PAC mobility T-score was 8.2 (95% CI, 6.3-10.1) points higher after HIHR vs. SNF. Adjusted Medicare costs were lower for the HIHR cohort (within 90 days, –$17,123; 95% CI, –$20,757 to –$13,490). Hospital LOS and odds for readmission did not differ between cohorts. The HIHR cohort demonstrated better functional outcomes and lower posthospital costs. HIHR may be a high-value option for patients attributed to a Medicare ACO who have moderate medical complexity and moderate functional deficits at the time of hospital discharge.

Association of Medicaid Accountable Care Organizations and Postpartum Mental Health Care Utilization
Date: January 7, 2025
Source: Health Services Research
This study examined the association of Massachusetts Medicaid ACO implementation with changes in mental health care utilization in the postpartum period. The study examined care for people with a birth covered by Medicaid or private insurance and used a difference-in-differences design to compare differences before and after Medicaid ACO implementation for those with Medicaid versus those with private insurance. The primary outcome was a binary measure of having at least one outpatient mental health care visit in the 6 months postpartum. The study included 107,813 births (53.0% Medicaid, 47.0% private). About 8% of women had at least one outpatient mental health visit in the 6 months postpartum, with similar rates among those with Medicaid versus those with private insurance pre-ACO implementation (7.9% Medicaid versus 7.7% private). An increase in utilization among privately insured individuals and a decrease among Medicaid beneficiaries post-ACO implementation was observed. Regression-adjusted difference-in-differences estimates indicate that Medicaid ACO implementation was associated with a 1.3 percentage point [pp] decrease (95% confidence interval: 1.3 pp, −0.5 pp; p < 0.01) in the probability of having an outpatient mental health visit for those with Medicaid. Future research should determine whether this increased disparity in mental health care utilization persists with maturation of the ACO delivery model.

Use Of Patient Health Survey Data for Risk Adjustment to Limit Distortionary Coding Incentives in Medicare
Date: January 2025
Source: Health Affairs
A core problem with the current risk-adjustment system in Medicare Advantage and ACO programs—the Hierarchical Condition Categories (HCC) model—is that the inputs (coded diagnoses) can be influenced for gain by risk-bearing plans or providers. Using existing survey data on health status (which provide less manipulable inputs), researchers found that the use of a hybrid risk score drawing from survey data and a scaled-back set of HCCs would, in addition to mitigating coding incentives, modestly lessen risk-selection incentives, strengthen payment incentives to deliver efficient care, allocate payment across ACOs more efficiently according to markers of population health that are not as affected by practice patterns or coding efforts, and redistribute payment in a manner that supports equity goals. Although sampling error and survey nonresponse present challenges, analyses suggest that these should not be prohibitive. Overall, this proof-of-concept analysis suggests that using survey data to improve risk-adjustment performance is a promising strategy that merits further development.