614 SURGERY STUDIES HAVE ESTIMATED

that one half to two thirds of hospital adverse events are attributable to surgi-cal care.1-3 More than half of these events appear preventable.3-5 However, little is known about the human and systems factors that underlie such errors in surgery. The surgical management of disease is complex and difficult. Observers describe a large variety of organizational and human factors that contribute to poor surgical outcomes, including surgeon inex-perience,6-8 low hospital volume for an operation,9-11 excessive workload,12 fatigue,13 poor technology,14 insufficient supervision of trainees,15 inadequate hospital systems,16 poor communica-tion among staff,17 time of day,14 and bureaucracy or administrative failures.18 To target interventions and policies, clinicians, administrators, and regula-tors have sought to identify which of these factors are implicated most frequently in surgical error. However, determining the relative importance of the various factors has proven extremely diffi-cult. Chart review and observational studies have not revealed sufficiently detailed information about a large enough number of events to discern the underlying patterns.3,19-22 By contrast, in-depth investigations of incidents involving error have allowed identification of “root causes ” in individual cases,23 but have been too time and labor intensive to replicate on a larger scale. Recently, policymakers in the United States and elsewhere have advocated both mandatory and voluntary error reporting systems to collect the desired information.22 These reporting systems face significant operational challenges, particular-ly in obtaining more than sporadic participation by clinicians. Analysis of errors reported by surgeons at three teaching hospital