The GRADE approach, Part 1: how to assess the certainty of the evidence.

The certainty of the evidence for interventions is the certainty or confidence that the true effect is within a particular range or relative to a threshold. In the new pyramid of evidence, systematic reviews represent the magnifying glass through which this certainty is evaluated. The GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach arises in response to the existence of multiple evidence classification systems, and it offers a transparent and structured process to develop and present summaries of evidence considering its certainty and, in a second step, the strength of the recommendations that they inform. The GRADE process begins with an explicit question that includes all important and critical outcomes explicitly. The main domains used to assess the certainty of the evidence are risk of bias, inconsistency, indirectness of evidence, imprecision, and publication bias. The factors that can increase the certainty of the evidence are dose-response gradient, large magnitude of an effect, and effect of plausible residual confounding. Finally, the Summary of Findings tables summarize the process in a simplified way and with controlled language. This narrative reviews purpose is to address the GRADE approachs theoretical and practical underlying concepts in a simplified way and with practical examples.