Prospective collection of data provides better assessment of risk

Prospective collection of data may be the best method to assess the rate of adverse and preventable events and the impact of risk reduction programmes. In a study on 778 patients, Michel and colleagues (p 199) compared the effectiveness, reliability, and acceptability of estimating rates of adverse events, and of preventable adverse events, using three methods: cross sectional, prospective, and retrospective. The prospective and retrospective methods identified similar numbers of medical and surgical cases (70% and 66%), but the prospective method identified more preventable cases, had good reliability, and an acceptable workload. The cross sectional method had a large number of false positives and identified none of the most serious events. No method was appropriate for obstetrics.