ACO Patient Population Attribution: Prospective vs Performance Year Methods

Attributing patients to an accountable care organization retrospectively may be more beneficial than prospective attribution, according to a study in Health Affairs.

The authors compared two methods of defining a patient population an ACO will be accountable for:

1. Prospective method. In this method, patients who received care by the providers in the previous year are attributed to the ACO for the current performance year.

2. Performance year method. In this method, an ACO defines its patient population at the end of the year based on the patients who received care at the ACO during that performance year.

To compare these two methods, the authors simulated a set of ACOs using Medicare fee-for-service claims data from 2008 and 2009. Here are comparisons in three areas related to patient attribution:

Percent of assigned patients who did not receive care at the ACO in the performance year

Prospective method: 17 percent
Performance year method: 0 percent

Percent of patients who received care at an ACO in the performance year but were not assigned to the ACO
Prospective method: 55 percent
Performance year method: 43 percent
Note: Many patients who visited an ACO's specialists were not attributed to the organization because they visited a primary care physician in a different ACO. The attribution method in the simulation looked at primary care over specialist care visits.

Percent of patients' total medical visits that occurred at the ACO
Prospective method: 68 percent
Performance year method: 74 percent

The authors concluded, "Performance year attribution may more fully and accurately reflect an ACO's patient population and may better position an ACO to achieve shared savings."

More Articles on ACOs:

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Study: ACO Metrics Fall in 6 Main Categories

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