Reliability of medical group and physician performance measurement in the primary care setting.

BACKGROUND: Performance reporting is increasingly focused on physician practice sites and individual physicians. OBJECTIVE: To assess the reliability of performance measurement for practice sites and individual physicians. RESEARCH DESIGN: We used data collected across multiple payers as part of a statewide measurement collaborative to evaluate the observed measure reliability and sample size requirements to achieve acceptable reliability of 4 Health Care Effectiveness Data and Information Set measures of preventive care and 10 Health Care Effectiveness Data and Information Set measures of chronic care across 334 practice sites. We conducted a parallel set of physician-level analyses using data across 118 primary physicians practicing within a large multispecialty group. MEASURES: Observed reliabilities and estimated sample size requirements to achieve reliability >/=0.70. RESULTS: At the practice site level, sample sizes required to achieve a reliability of 0.70 were less than 200 patients per site for all 4 measures of preventive care, all 4 process measures of diabetes care, and 2 outcomes measures of diabetes care. Larger samples were required to achieve reliability for cholesterol screening in the presence of cardiovascular disease (n = 249) and use of appropriate asthma medications (n = 351). At the physician level, less than 200 patients were required for all 4 measures of preventive care, but for many chronic care measures the samples of patients available per physician were not sufficient to achieve a reliability of 0.70. CONCLUSION: In a multipayer collaborative, sample sizes were adequate to reliably assess clinical process and outcome measures at the practice site level. For individual physicians, sample sizes proved adequate to reliably measure preventive care, but may not be feasible for chronic care assessment