We welcome Dr Walshe's review of the study of adverse events.¹ Dr Walshe points out the usefulness of studies of adverse events, but also the need to be cautious when they are used as measures of health care quality. We think that this article underlines the major methodological issue in studies of adverse events—namely, the lack of a standardised definition. Until this point is resolved, the practical applications of the concept of adverse events will be limited. Definitions of this term are frequently grouped into two categories—restrictive and broader. Restrictive …