Detecting differences in quality of care: the sensitivity of measures of process and outcome in treating acute myocardial infarction

The merits or otherwise of publishing hospital specific death rates are much debated. This article compares the relative sensitivity of measures of process and outcome to differences in quality of care for the hospital treatment of myocardial infarction. Aspects of hospital care that have a proved impact on mortality from myocardial infarction are identified, and the results from meta-analysis and large randomised controlled trials are used to estimate the impact that optimal use of these interventions would have on mortality in a typical district general hospital. Sample size calculations are then performed to determine how many years of data would be needed to detect significant differences between hospitals. A comparison is then made with the amount of data that would be needed to detect significant differences if information about process of care was being collected. Process measures based on the results of randomised controlled trials were found to be able to detect relevant differences between hospitals that would not be identified by comparing hospital specific mortality, which is an insensitive indicator of the quality of care.

Dissatisfaction is widespread with the mechanisms currently being used to monitor performance in the NHS. Contracts between purchaser and provider are dominated by finance and activity. Specifications that relate to the quality of care often either are unmeasurable or refer to limited aspects of care--such as waiting times--which, while relevant, do not fully reflect the quality of clinical care. Purchaser performance is monitored by a similarly barren tool, the efficiency index, which encourages increased activity per pound spent with no regard to the benefits or adverse effects of the measured activity on health.1

One response to these criticisms has been to encourage the use of routine measures of outcome, such as death rates, to compare hospital performance. A recent example of this has …