In analyzing a university-based program to educate physicians about proper medication use, we sought to measure whether physician background characteristics and the quality or number of educational exposures influenced the rate of relinquishment of inappropriate prescribing. A sample of 435 doctors was randomized to control and experimental groups; interventions consisted of printed educational materials and face-to-face visits by clinical pharmacists. The program sought to reduce inappropriate use of three drug categories: propoxyphene, peripheral/cerebral vasodilators, and cephalexin. Outcome data included the total volume (tablets/capsules) of these drugs prescribed through Medicaid by each study physician 9 months before and after the program. We estimated average changes in prescribing levels by experimental and control physicians within each physician subgroup (e.g., board-certified versus uncertified), adjusting for prescribing level in the same 9 months of the previous year. The results indicated that the rate of prescribing change was independent of most physician background characteristics studied, including age, board certification, specialty, rural versus urban practice, intensity of previous target drug use, and size of Medicaid practice. Experimental effects were highly significant (-9% to -20%, P