Is it better to be cared for by a tired intern who knows your case or a rested intern who does not? Though some studies have shown that interns working traditional long hours (shifts of 24 hours or more) make more mistakes than those working reduced hours, others have shown that work-hour limits cause delays in tests and other preventable complications. In fact, a recent study in the Journal of the American Medical Association found no evidence that new reductions in work hours improved the quality or safety of patient care.

Patient safety is also heavily influenced by the number of patients that interns are responsible for. Because interns’ patient loads have not decreased (and have probably increased) in recent years, rigid work-hour restrictions may also be aggravating safety problems by compressing work into shorter shifts.

Long hours and hard work have been features of medical training since the modern residency program had its beginnings at the Johns Hopkins Hospital in Baltimore in the late 19th century. As the medical historian Kenneth M. Ludmerer details in his recent book “Let Me Heal,” an authoritative account of the residency system in the United States, teaching hospitals and medical residents have always had an implicit contract: Hospitals provide patients (often indigent ones) on whom young doctors learn their craft; in return, young doctors provide cheap labor to keep these institutions running.

“The only thing that has changed,” Dr. Ludmerer told me recently, “is the nature of the exploitation.” In earlier generations, he explained, young doctors were saddled with considerable manual chores — drawing blood, inserting intravenous lines, transporting patients and so on. In the past two decades, these chores have been replaced by a new kind of scut work: treating a large number of patients (to help maintain hospital “throughput”) while juggling an expanding load of administrative chores.

This workload has become even harder to manage because of rules — designed to provide respite — that mandate that interns must leave the hospital immediately after completing a shift. Rushing to finish their work can cause interns to make mistakes and order unnecessary tests to compensate for a lack of time to think through a difficult case.