This observational study analyzed surgical outcomes before and after 2011 ACGME duty hours reform using data from the American College of Surgeons National Surgical Quality Improvement Program. Researchers applied difference-in-differences analysis, which can account for some of the uncertainty of nonrandomized data, a common concern in patient safety research. They assessed changes in surgical mortality and complication rates before and after implementation of duty hours restrictions in teaching hospitals. The authors compared this difference with mortality and complication rates during the same time period in nonteaching hospitals. Any variation between teaching and nonteaching sites could be attributed to the effects of duty hours, since the authors accounted for case mix and comorbidities. No differences in patient outcomes were observed, adding to the evidence that duty hours restrictions do not improve patient outcomes. Researchers also found no change in trainee examination scores, despite concerns that duty hours adversely impact trainee education. An editorial discussing this work and a companion study urge flexibility in duty hours for physicians in training.