Variation in the rates of adverse events between hospitals and hospital departments.

OBJECTIVE The objective of this study was to analyze the variation in the rates of adverse events (AEs), and preventable AEs, between hospitals and hospital departments in order to investigate the room for improvement in reducing AEs at both levels. In addition, we explored the extent to which patient, department and hospital characteristics explain differences in the rates of AEs. DESIGN Structured retrospective patient record review of hospital admissions. SETTING Twenty-one Dutch hospitals. Population A representative random sample of 7113 hospital admissions in 2004. MAIN OUTCOME MEASURES Variation in AEs, and preventable AEs, between hospitals and hospital departments and the explanatory factors of the variation. RESULTS The rates of AEs varied between hospitals (P = 0.05) and hospital departments (P < 0.05). The rates of preventable AEs only varied significantly between hospital departments. The clustering of preventable AEs in hospital departments was more than twice that found in hospitals (ICC 9.5 versus 3.5%). The type of hospital explained 35% of the inter-hospital variance in AEs. Patient and department characteristics explained 23% of the inter-department variance in preventable AEs. CONCLUSIONS In addition to interventions to improve the overall patient safety within a hospital, interventions tailored for specific departments are necessary to reduce their patient safety risks. Monitoring and comparing the performance of hospitals should not be limited to the hospital level, but should be extended to the individual department since there can be significant differences in the rates of preventable AEs between different departments within the same hospital.