1. From the Division of General Internal Medicine and the Leonard Davis Institute of Health Economics, University of Pennsylvania, Philadelphia (H.G., D.P.); Pharmacia and Upjohn Inc., Kalamazoo, Mich (R.W.); the Department of Neurosurgery and the Virginia Neurological Institute, University of Virginia, Charlottesville, Va (W.A., N.K.); and the Clinical Economics Research Unit, Division of General Internal Medicine, Georgetown University Medical Center, Washington, DC (K.S.).