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The first full year of contracts for accountable care organizations in the Medicare Shared Savings Program led to reductions in spending, but those cuts dropped significantly in the second cohort, a new study shows.

Researchers analyzed Medicare claims data from 2009 through 2013 to compare changes in spending and quality performance before ACO contracts began, and when MSSP’s 2012 and 2013 ACO cohorts entered the program. Spending trends were similar for the 220 ACOs in the MSSP cohorts and a control group in the time before the contracts kicked in, the study’s authors reported.

The first cohort, which included ACOs that entered the program in mid-2012, saved $144 per beneficiary, or 1.4%, compared to the control group. The second cohort, which entered the program in 2013, yielded $3 in savings per beneficiary when compared to the control.

The savings were greater for independent primary care groups, researchers noted, compared to those in hospital-integrated groups. ACOs participating in a MSSP contract also showed improved performance on select quality measures, and unchanged performance on others.

The study was published online Thursday in the New England Journal of Medicine.