Following Shipman: a pilot system for monitoring mortality rates in primary care

As part of the investigations into the crimes of Harold Shipman, it has become clear that there is little monitoring of deaths in general practice. By use of data on annual deaths at family physician and practice level for five English health authorities for 1993-99, we investigate whether cumulative sum charts (a type of statistical process control chart) could be used to create a workable monitoring system. On such charts, thresholds for deaths can be set, which, if crossed, may indicate a potential problem. We chose thresholds based on empirical calculations of the probabilities of false and successful detection after allowing for multiple testing over physicians or practices. We also statistically adjusted the charts for extra-Poisson varition due to unmeasured case mix. Of 1009 family physicians, 33 (including Shipman) crossed the alarm threshold designed to detect a 2 SD increase in standardised mortality, with 97% successful detection and a 5% false-alarm rate. Poor data quality, plus factors such as the proportion of patients treated by these physicians in nursing homes or hospices are likely explanations for most of these additional alarms. If used appropriately, such charts represent a useful tool for monitoring deaths in primary care. However, improvement in data quality is essential.