The Effect of Clinical Volume on Annual and Per-Patient Encounter Medical Malpractice Claims Risk.

OBJECTIVES: The relationship between medical malpractice risk and one of the fundamental characteristics of physician practice, clinical volume, remains undefined. This study examined how the annual and per-patient encounter medical malpractice claims risk varies with clinical volume. METHODS: Clinical volume was determined using health insurance charges and was linked at the physician level to malpractice claims data from a malpractice insurer. The annual medical malpractice claims risk was expressed as the percent of physicians with a malpractice claim, and the per-encounter medical malpractice claims risk was expressed as malpractice claims per 1000 patient encounters. Both of these malpractice claims risk metrics were analyzed as a function of clinical volume, using linear and spline regression. RESULTS: As clinical volume increased, the percent of physicians with a malpractice claim increased linearly. Among all physicians studied, for each decile increase in clinical volume, there was a 0.373% increase in physicians with a malpractice claim (95% confidence interval, 0.301%-0.446%; P < 0.0001). As clinical volume increased, the rate of malpractice claims per 1000 patient encounters decreased. This relationship between clinical volume and per-encounter claims risk was nonlinear. There was a clinical volume threshold, below which decreasing clinical volume was associated with increasing per-encounter claims risk, and above which claims risk no longer significantly varied with increases in clinical volume. CONCLUSIONS: Clinical volume is a crucial determinant of physician malpractice risk, with higher-volume physicians having higher annual risk but lower per-encounter risk. Clinical volume data should be incorporated into analyses of malpractice risk.