Adverse events: The more you search, the more you find

Physicians rely on compendia and product inserts to learn about medication-related harms. These materials offer litanies of possible adverse events, sometimes accompanied by an estimate of how often those events might occur. From whence are the estimates derived? What do they really mean? How can we better measure and understand how many and what kinds of harms may be caused by medications? In this issue, Bent and colleagues remind us that how we define and look for problems markedly affects the numbers of harms that patients report