GRADE guidelines: 3. Rating the quality of evidence
This article introduces the approach of Grading of Recommendations Assessment, Development and Evaluation (GRADE) to rating quality of evidence in health research. GRADE specifies four categories - high, moderate, low, and very low -that are applied to a body of evidence, not to individual studies. In the context of a systematic review, quality reflects our confidence that the estimates of the effect are correct.
In the context of recommendations, quality reflects our confidence that the effect estimates are adequate to support a particular recommendation. Randomised trials begin as high-quality evidence, observational studies as low quality. “Quality” as used in GRADE means more than risk of bias and so may also be compromised by imprecision, inconsistency, indirectness of study results, and publication bias. In addition, several factors can increase our confidence in an estimate of effect. GRADE provides a systematic approach for considering and reporting each of these factors. GRADE separates the process of assessing quality of evidence from the process of making recommendations. Judgments about the strength of a recommendation depend on more than just the quality of evidence.
This paper is part of the 2011 Journal of Clinical Epidemiology collection of articles that provide a guide for systematic review and health technology assessment authors, guideline panelists and methodologists on how to apply the GRADE methodology framework in more detail.