Establishing Thresholds for Adverse Patient Outcomes

OBJECTIVE: To establish thresholds for adverse patient outcomes in the absence of knowledge of patient illness severity indices. OUTCOMES: Pulmonary embolism, unplanned return to operating rooms, unplanned readmissions, clean and contaminated wound infections, and hospital-acquired bacteraemia. DESIGN: Analysis of results of surveys of hospitals in Australia by the Australian Council on Healthcare Standards following the introduction of clinical performance measures into the Accreditation process. SETTING: Acute care hospitals in Australia undergoing Accreditation surveys in 1993 and 1994. METHODS: Stratification of hospitals into small (1-99 beds), medium (100-199 beds), and large (> or = 200 beds), calculation of mean rates for the above outcomes in each group, and establishment of thresholds based on two standard errors from the mean. RESULTS: The mean rate of occurrence of incidents was higher for larger hospitals. Thresholds were generally lower for smaller and higher for larger hospitals. CONCLUSIONS: Bed-size is a useful index for "flagging" peer group variation. The methodological issues in establishing thresholds and their implications in monitoring the quality of care in hospitals are discussed.