Inappropriate use of hospitals in a randomized trial of health insurance plans.

We examined geographic variation in the rate of inappropriate hospitalization and the effect of cost sharing on that rate. The medical records of 1132 adults hospitalized in a randomized trial of health insurance plans were reviewed by two physicians who were blinded to the patients' insurance plan. They judged 23 percent of the admissions to be inappropriate and an additional 17 percent to have been avoidable by the use of ambulatory surgery. The percentage of inappropriate admissions varied among six sites (from 10 to 35 percent), but areas with low total admission rates did not necessarily have low proportions of inappropriate admissions. In plans with cost sharing for all services, 22 percent of admissions and 34 percent of hospital days were classified as inappropriate, as compared with 24 percent of admissions and 35 percent of hospital days in the plan under which care was free to the patient (these differences were not statistically significant). Our data show that a substantial fraction of hospitalization is potentially avoidable. Because cost sharing did not selectively reduce inappropriate hospitalization, it is important to develop other mechanisms to do so.