Understanding Hierarchies of Evidence and Grades of Recommendation

Hierarchies of evidence have been established to assist clinicians in judging the overall quality of studies and for developing grades of recommendation. These hierarchies take into account both study design and study methodology, among other characteristics, to rank studies into several levels. Studies of a sound design and methodological rigor are less subject to bias and rank highly in the hierarchy, whereas those studies vulnerable to biased results rank progressively lower in the hierarchy. It is on the basis of these hierarchies that grades of recommendation and clinical practice guidelines can be established to facilitate the practice of evidence‐based medicine.