A Practical Guide to Assigning Levels of Evidence
James G. Wright, MD, MPH, FRCSC

Evidence-based medicine uses the best available evidence to make decisions with patients. The highest-quality evidence is well-designed randomized trials. The most compelling example of the power of trials comes from pediatric oncology. The improvement in the survival rate of children with cancer from 10% to 90% has been attributed almost exclusively to multiple randomized trials1. Since January 2003, every clinical article published in The Journal of Bone and Joint Surgery has been assigned a level-of-evidence rating2. Levels of evidence provide a concise and simple appraisal of study quality. The essence of levels of evidence is that, in general, controlled studies are better than uncontrolled studies, prospective studies are better than retrospective studies, and randomized studies are better than nonrandomized studies. Levels of evidence have multiple purposes. First, levels of evidence provide the readers of The Journal with a rapid appraisal of study quality. Although a complete critical appraisal is required to determine study quality3, readers generally find higher levels of evidence more compelling. Second, levels of evidence for multiple studies evaluating a clinical question can be summarized as a “grade of recommendation.” Grades of recommendations, such as A, B, C, or I, provide an overall appraisal of the quality of literature for or against a treatment recommendation4. Third, levels of evidence can be used to develop practice guidelines and performance measures. In an era of pay-for-performance, whereby evidence-based interventions receive higher reimbursement5,6, understanding levels of evidence is important for surgeons.

In considering levels of evidence, surgeons need to know that the evaluation is reliable and valid. Several studies have shown that the assignment of levels of evidence is reliable7,8. The first table explaining the level-of-evidence ratings, published in the January 2003 issue of The …

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