Table 3.

The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system for grading evidence: reflection on quality by study type (6)

CharacteristicStudy
Patient- and population-level evidenceRandomized clinical trials start with a high-quality GRADE but may be graded down after evaluation of study limitations, inconsistency of results with other randomized clinical trials, lack of direct evidence, lack of precision, or reporting bias
Population-level evidenceObservational studies start with a low-quality GRADE, but grading upward may be warranted with large treatment effects or evidence of dose response
  • GRADE quality of evidence definitions: high quality, additional research is very unlikely to change confidence in the estimate of effect; moderate quality, additional research is likely to have an important impact on confidence in the estimate of effect and may change the estimate; low quality; additional research is very likely to have an important impact on confidence in the estimate of effect and is likely to change the estimate; very low quality, any estimate of effect is very uncertain.