The appraisal of medical scientific evidence

Abstract

A ny doctor would prefer to base his therapeutic approach on the best existing scientific evidence. We could name it MABBEE-Medical Approach Based on the Best Existing Evidence. The problem is how to define what is good scientific evidence and what is not. We understand that nowadays there is reasonable consensus on accountable methodologies for the critical appraisal of medical literature. The reader may easily find them in the literature of these last two decades (1,2,3,4,5,6), and improve his/her skills through the American College of Physicians Journal Club, which is a supplement to the Annals of Internal Medicine. However, it is important to point out some features of the model of the studies which generate the evidences to allow the development of "MABBEE medicine". The randomized double-blind control trial with an adequate sample size and quality control is the ideal design to compare placebo to any treatment, or different types of clinical or surgical treatments. Although this seems obvious, it has still not been widely applied to medical practice in this country. Reasoning based on experience, case reports, and retrospective studies are still very common in Medical Journals and meetings. Another method of obtaining good evidence is the systematic review of medical treatments followed by a statistical summary named meta-analysis. This type of research should include all the published and unpublished controlled clinical trials with good standards. The typical odds ratio-the final result-usually represents the best evidence regarding that specific treatment until the moment the meta-analysis was properly completed. However the consistency of the results depends on the clinical trials found in the literature. Publication bias, which is the tendency by some journal editors not to publish clinical trials with negative results, affects not only the authors submitting the papers but also the systematic review preparation, and finally the doctors interested in the best evidence-based medicine, which, as a consequence, affects the patients. Prospecti ve cohort studies are much better than retrospecti ve studies, because they allow for stronger conclusions. A prospective study performed in developing countries has better chances of earning confidence. Diagnostic tests must be assessed regarding their utility. That means the adoption of an excellent gold standard, definition of cutoff points, calculation of sensitivity, specificity, and predictive values, and describing confidence intervals. Comparisons with a traditional diagnostic test (Receiver Operating Characteristics-ROC) can also be made. For more details the reader may be referred to (2) and (6).