Students of evidence-based medicine often try unsuccessfully to commit to memory a particular critical appraisal framework (often lengthy), or they have to depend on pocket cards and are lost without them. We have described a pedagogic aid: a flow diagram of an RCT, which has been developed over years of teaching residents. This diagram focuses on the steps in an RCT, and by drawing arrows, it highlights the biases possible at each step. This diagram serves as a framework on which the list of critical appraisal questions can be hung and is easy to remember.