For many years, people have been concerned that doctors in training (called residents) might be making mistakes because they do not get enough sleep when they are on duty at the hospital. The organization that is responsible for ensuring good learning conditions for residents made a rule: After July 2003, residents could spend no more than 80 hours per week at work. Moreover, they could spend no more than 24 consecutive hours at work without leaving the hospital. No one was sure how this new rule would affect patient care. On the one hand, residents would probably make fewer errors if they got more sleep. On the other hand, if a resident spends less time in the hospital, another resident must take care of his or her patients when the resident is away. The new resident probably will not know the patients' problems as well as the resident who has principal responsibility for the patients, which may increase errors in patient care.