Savings of MSSP ACOs May Be Overstated, Annals Study Finds

June 18, 2019

Medicare Shared Savings Program (MSSP) accountable care organizations (ACOs) cover more than 32 million lives and have been found to save money and improve quality in past research, but a new study in Annals of Internal Medicine is calling their success into question.

Medicare Shared Savings Program (MSSP), CMS’ accountable care organization (ACO) program, does not reduce spending or improve quality of care, according to a new study published in Annals of Internal Medicine.

With more than 900 contracts, ACOs cover more than 32 million US lives. ACOs are a broad, far-reaching, value-based reform effort, and under MSSP groups of hospitals, clinicians, and other providers voluntarily take on spending and quality outcome responsibilities for a certain population of fee-for- service Medicare beneficiaries. The results of the recent study challenge past claims that MSSP ACOs lower cost and improve quality.

The investigators analyzed a random 20% sample of claims data for Medicare fee-for-service beneficiaries age 65 and older. They evaluated the effect of MSSP on spending and quality of care by measuring total spending, 4 quality indicators, and hospitalization for hip fractures. Hip fractures served as a falsification outcome. The study also accounted for high-cost clinicians exiting ACOs.

The authors used adjusted longitudinal models to compare MSSP ACO participants with control beneficiaries. The models accounted for secular trends, market factors, and beneficiary characteristics. They also used the share of nearby clinicians in the MSSP as an instrumental variable. In the instrumental model, MSSP was not associated with changes in total spending, but MSSP was not associated with hip fracture hospitalizations in the instrumental model. Meanwhile, in the longitudinal model, MSSP was associated with a substantial decrease in hip fracture hospitalizations and a reduction in total spending.

The authors found that high-cost clinicians (those in the 99th percentile) had a 30.4% change of exiting MSSP. In fact, they found that spending trends before the start of the MSSP differed between beneficiaries who did enter the program and beneficiaries who did not enter the program.

“Together, our results suggest that improved quality and spending performance in this voluntary program may have been driven by nonrandom exit of clinicians and their patient panels from the MSSP,” they wrote.

This study contradicts past research, commissioned by the National Association of ACOs (NAACOS), that has shown that MSSP saved the government $542 million between 2013 and 2015, while ACOs as a whole grossed $1.84 billion in savings. However, a similar study conducted by CMS over the same time period found that ACOs increased Medicare spending by $344 million dollars.

The agency’s benchmarking methodology looked at how ACO spending differed from spending in the previous years, while NAACOS’ study analyzed how the spending of ACOs compared with providers not participating in ACOs at all.

NAACOS noted in a statement that two-thirds of the ACOs in the Annals study had 1 or 2 years of experience, and past research has shown that as ACOs gain more experience, they perform better and save more money.

"This paper is not an indictment of the real savings ACOs have generated, but further evidence of how the model is unfolding," NAACOS said in the statement. "We know ACOs on the whole are saving Medicare money. This has been verified by multiple independent studies, including by MedPAC, researchers at Harvard, and NAACOS. These savings can translate into tens of billions of dollars over time when compounded annually and considering growth of the ACO program and more experience leads to greater savings."


Markovitz AA, Hollingsworth JM, Ayanian JZ, Norton EC, Yan PL, Ryan AM. Performance in the Medicare Shared Savings Program after accounting for nonrandom exit: an instrumental variable analysis [published online June 17, 2019]. Ann Intern Med. doi:10.7326/M18-2539.