The critical appraisal of a randomised controlled trial (RCT) is one of the basic elements of clinical epidemiology and evidence-based medicine curricula. Various frameworks for critical appraisal have been proposed. The “Users' Guides” series in JAMA includes a framework for evaluating RCTs that consists of 12 questions grouped under 3 headings^{1, 2}:

• Are the results of the study valid?

• What were the results?

• Will the results help me in caring for my patients?

However, >20 published users' guides currently exist, and our experience shows that residents and clinicians attempting to pursue a practice that uses evidence-based medicine have 1 of 2 problems: either they try to memorise, without much success, all the questions from several of these guides, or they rely completely on small pocket cards that contain the pertinent questions and then find themselves lost if they misplace or forget those cards. Other groups have developed more general criteria. For example, the Newcastle Critical Appraisal Worksheet is a 3 × 10 grid that can be applied to any type of study, but it requires some basic knowledge of epidemiological terms and concepts.³

Over time, we've put together a flow diagram of RCTs and the points at which bias can creep in; this flow diagram serves as a memory aid and can act as a framework on which to “hang” whatever critical appraisal guide the user is most comfortable with. We have often found that the process of drawing this …