TABLE 1

GRADE System Definitions

Type of EvidenceQuality of Evidence
High: evidence based on randomized, controlled trialsHigh quality: additional research is very unlikely to change our confidence in the estimate of effect.
Low: evidence based on observational studiesModerate quality: additional research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Very low: any other evidenceLow quality: additional research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: Any estimate of effect is very uncertain.
  • Critiques (review articles and editorials) are ineligible for assessment by the GRADE system of evaluation.

    Adapted with permission from BMJ Publishing Group Ltd from Atkins D, Best D, Briss PA, et al; GRADE Working Group. BMJ. 2004;328(7454):1490.