During the past ten years, a number of changes have been implemented in emergency health care systems with the intention of reducing the mortality, morbidity, and cost of trauma in the United States. The cornerstone of such health care systems modifications has been the trauma center—a hospital that meets explicit criteria and is committed to excellence in the care of the critically injured. Another important and expensive change has been the increased use of helicopters to reduce the time between injury and surgical care, an issue germane to improving trauma outcome. Some 55 hospitals in the United States currently operate their own helicopter programs, and many others receive patients from public-service—operated rotorcraft.
Determining the impact of trauma centers and helicopters on trauma patient outcome has been hampered by the inability to control for case mix. Injury severity indices that correlate with patient outcome have recently been combined with state-of-the-art statistical