Which physician would get the credit?

As Medicare moves to develop a national physician P4P program, two assumptions underpin successful implementation: that claims data can be used to retrospectively assign patients to physicians or practices with primary responsibility for their care, and that physicians can be held responsible for a meaningful percentage of the patients they treat and the visits they bill for.

The reality, however, is that many different physicians and practices provide care to each elderly Medicare patient, so identifying which provider is responsible for which patient is difficult. Because of this, physicians also are unlikely to have a critical mass of patients who are their primary responsibility, and about a third of the patients they would be held responsible for will switch to a different provider the next year anyway, the study found.