Principles of Evidence‐based Dermatology

Michael Bigby, Hywel C. Williams


Evidence‐based medicine (EBM) is the integration of best research evidence with clinical expertise and patient values. Practising EBM consists of five steps: (i) formulating a well‐built clinical question generated from a patient encounter; (ii) searching for valid external evidence; (iii) critically appraising that evidence for relevance and validity; (iv) applying the results of that appraisal of evidence back to the patient; and (v) recording the information for future use. An important principle of EBM is that the quality (strength) of evidence is based on a hierarchy of evidence. The order of the hierarchy of evidence is dependent on the type of question being asked. The hierarchy of evidence consists of results of well‐designed experimental studies such as randomized controlled trials (especially if the studies have results of similar magnitude and direction, and if there is homogeneity among studies), results of observational studies, case series, expert opinion and personal experience, in descending order.
Keywords randomized controlled trial, systematic review, meta‐analysis, Cochrane Library, MEDLINE, EMBASE, intent to treat, case–control, cohort, odds ratio, relative risk, likelihood ratio, risk difference, number needed to treat, number needed to harm


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