Background: Comparison of the outcomes of care provided by hospitals is a growing trend. Outcomes need to be distinguished into those attributable to the practice of hospitals and those that arise from differences in the characteristics of patients and the underlying morbidity of the populations for whom hospitals provide care. We explored these issues for deaths in hospital or within 30 days of discharge after acute myocardial infarction in Scotland, UK.
Methods: We used records from December, 1992, to November, 1993, for 14,359 episodes of acute myocardial infarction, the death records of those who died, and 9391 death records for individuals who died after acute myocardial infarction but who had not been in hospital in the 30 days before death. Hospital discharge records were taken from the Scottish Morbidity Records. The outcomes we investigated were all-cause mortality within 30 days of discharge from hospital, and death from acute myocardial infarction at any time during the study period. We estimated separately effects attributable to patients' characteristics, hospitals, and areas of residence with multilevel modelling.
Findings: We found significant differences between hospitals by age, sex, and medical history. The odds ratios for death ranged from 0.62 (95% CI 0.50-0.80) to 1.28 (1.07-1.59), relative to the average performance for Scotland as a whole. Analysis including area of residence, deaths occurring out of hospital, and more detailed information about patients showed no significant differences between hospitals for patients aged 70 years. By postcode area, there was a strong association between out-of-hospital deaths and deaths in hospital or shortly after discharge.
Interpretation: Hospital outcomes may vary from one subgroup of patients to another and should be assessed independently of patients' areas of residence. Measures of performance that do not provide valid comparisons could diminish public confidence in hospital services.