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Study Objective: To determine the effect of displaying previous results of diagnostic tests on the ordering of selected outpatient tests.

Design: Sixteen-week controlled trial with a 13-week preintervention and 8-week post-intervention observation periods. Patients were randomly assigned to intervention or control groups so that each physician was his or her own control. Only scheduled visits were included. Randomization occurred before the pre-intervention observation period.

Setting: Academic primary care general medicine clinic affiliated with an urban general hospital.

Subjects: Pre-intervention period: 111 physicians (97 internal medicine residents, 14 faculty internists), 4683 patients, 5942 scheduled visits. Intervention period: same 111 physicians, 5946 patients, 8148 visits. Post-intervention period: 76 physicians (62 residents, 14 faculty), 2571 patients …