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Table 8 The GRADE system for assessing the quality of evidence

From: SUPPORT Tools for evidence-informed health Policymaking (STP) 16: Using research evidence in balancing the pros and cons of policies

Evaluating the quality of evidence requires judgements about the extent to which one can be confident that an estimate of effect is correct. GRADE provides a systematic and transparent approach to making these judgements for each outcome important to a decision [12]. The judgements are based on the type of study design (randomised trials versus observational studies), the risk of bias (study limitations), the consistency of the results across studies, and the precision of the overall estimate across studies. Based on these considerations for each outcome, the quality of the evidence is rated as high, moderate, low, or very low, using the following definitions:
High Confident that the true effect lies close to that of the estimate of the effect
Moderate The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different
Low The true effect may be substantially different from the estimate of the effect
Very low Very uncertain about the estimate