Safety in numbers: the development of Leapfrog's composite patient safety score for U.S. hospitals.

OBJECTIVE To develop a composite patient safety score that provides patients, health-care providers, and health-care purchasers with a standardized method to evaluate patient safety in general acute care hospitals in the United States. METHODS The Leapfrog Group sought guidance from a panel of national patient safety experts to develop the composite score. Candidate patient safety performance measures for inclusion in the score were identified from publicly reported national sources. Hospital performance on each measure was converted into a "z-score" and then aggregated using measure-specific weights. A reference mean score was set at 3, with scores interpreted in terms of standard deviations above or below the mean, with above reflecting better than average performance. RESULTS Twenty-six measures were included in the score. The mean composite score for 2652 general acute care hospitals in the United States was 2.97 (range by hospital, 0.46-3.94). Safety scores were slightly lower for hospitals that were publicly owned, rural in location, or had a larger percentage of patients with Medicaid as their primary insurance. CONCLUSIONS The Leapfrog patient safety composite provides a standardized method to evaluate patient safety in general acute care hospitals in the United States. While constrained by available data and publicly reported scores on patient safety measures, the composite score reflects the best available evidence regarding a hospital's efforts and outcomes in patient safety. Additional analyses are needed, but the score did not seem to have a strong bias against hospitals with specific characteristics. The composite score will continue to be refined over time as measures of patient safety evolve.