Monitoring ambulatory care: impact of a surveillance program on clinical practice patterns in New York City.

Administrative records of the Title XIX (Medicaid) Program of New York City were reviewed to determine the impact of a surveillance system introduced to monitor physician billing. Billing patterns of the physicians subject to program sanctions, as well as the larger universe of all participating New York City physicians, showed changes coincident with the introduction of the surveillance program: utilization of x-rays, lab tests, injections, and first visit billing decreased.