In 1999, the U.S. Institute of Medicine reported that mistakes in U.S. hospitals are alarmingly frequent. This report relied on studies that used doctors and nurses to review patients' medical records to identify mistakes. In these studies, the doctors and nurses looked at the medical records to first decide whether a patient had experienced a complication. Second, they had to decide whether the complication was related to medical care. Third, they needed to decide whether the complication was an expected side effect or was caused by someone's mistake. Judging whether someone made a mistake can be difficult when you have only the information in the patient medical record.