Today, a new set of rules goes into effect, limiting first-year residents, also called interns, to 16-hour shifts. The rules, put in place by the private nonprofit Accreditation Council for Graduate Medical Education, are intended to prevent medical errors resulting from sleep deprivation. Second- and third-year residents will still be permitted to work 28 hours at a time. But in the last four hours, they can't take on new patients. Debate has been raging for years over this issue--and the new rules haven't ended it. Supporters of long shifts say residents gain invaluable experience through longer hours and managing the fatigue that inevitably comes with practicing medicine. They say patients are protected because residents, who make up almost a quarter of physicians working in hospitals, are closely supervised. Critics, however, cite research showing that doctors become so tired during long shifts that their performance deteriorates. They are no different in that respect from workers in other industries, according to decades of studies linking exhaustion to accidents and errors.