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Table 12.2.a: 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