Skip to Main Content

Literature Review: GRADE System

GRADE System for Systematic Reviews

The Grades of Recommendation, Assessment, Development and Evaluation (GRADE) for Systematic Reviews

GRADE defines the quality of a body of evidence as the extent to which one can be confident that an estimate of effect or association is close to the quantity of specific interest.”1

The GRADE system entails an assessment of the quality of a body of evidence for five factors:

  • Within-study risk of bias (methodological quality)
  • Directness of evidence
  • Heterogeneity (any kind of variability among studies)
  • Precision of effect estimates
  • Risk of publication bias

Levels of quality of a body of evidence in the GRADE approach


Underlying methodology

Quality rating

Randomized trials; or double-upgraded observational studies.


Downgraded randomized trials; or upgraded observational studies.


Double-downgraded randomized trials; or observational studies.


Triple-downgraded randomized trials; or downgraded observational studies; or case series/case reports.

Very low


The highest quality rating is for randomized trial evidence.

  • Randomized trial evidence can be downgraded  to moderate, low, or very low quality, depending on limitations, e.g.:
    • Randomization sequence was not concealed from the clinicians and researchers
    • The people involved in the study discovered which treatments were given to which patients
    • Over 50% of their patients were lost for follow-up
  • Conversely, observational studies may be upgraded if they produce large effects with no obvious bias

Information Sources: