During several years of teaching critical appraisal at both the undergraduate and postgraduate levels, I have used a modification of the number needed to treat (NNT). The COPE—the Cost of Preventing an Event—is a “back-of-the-envelope,” user friendly, cost effectiveness analysis for clinicians and policy makers. Economic evaluations can be defined as the “comparative analysis of alternative courses of action in terms of both their costs and their consequences.”¹ These analyses can be complex and sensitive to particular population groups and health systems and are often unavailable for clinicians (especially in developing nations). Traditionally, economists have used 1 of 5 methods for economic analysis: cost analysis, cost minimisation, cost effectiveness, cost utility, and cost benefit analyses.¹ The COPE is an approximate cost effectiveness statistic that can be calculated by clinicians for a new drug where a full economic evaluation is not available but where a randomised …