We appreciate Dr. Rifkin's firsthand experience and reactions to our study. Because this was a retrospective, observational study, we could not draw any firm conclusions about causality. Nonetheless, we fully agree with Dr. Rifkin that several factors, including increased supervision by senior residents, fellows, and attending physicians, probably played a role in the outcomes we observed.

The fact that the program schedule was revamped after the study period is particularly interesting given that we could not detect any evidence of harm to patients. This illustrates the importance of confirming (or challenging) conventional wisdom with carefully conducted studies.

In constructing schedules, program directors must balance many competing demands, including patient care, education, and resident well-being. Our study was designed to provide evidence only about the effect of work-hour regulation on patient care. We agree with Dr. Rifkin that further study of all aspects of work-hour regulation—using different approaches to regulation, at several sites, and over long periods—is essential.