TABLE 1.

Credibility assessment criteria for meta‐analyses of observational studies and Mendelian randomization studies

Evidence category	Criteria
Meta‐analyses of observational studies
Convincing (class I)	P < .001; >1000 cases; P < .05 in the largest study A 95% PI that excluded the null; I2 < 50% No evidence of small‐study effect (P > .10); and no excess significance bias (P > .10)
Highly suggestive (class II)	P < .001; >1000 cases P < .05 in the largest study
Suggestive (class III)	P < .001; >1000 cases
Weak (class IV)	P < .05
No association	P ≥ .05
Mendelian randomization study
Evidence of causality	P < .05 or threshold set up by individual study due to multiple testing; evaluated pleiotropy but have no evidence of directional pleiotropy.
Likely noncausal	P > .05 or threshold setup by individual study due to multiple testing; Power ≥0.8; consistent evidence between main MR analysis and sensitivity analyses; evaluated pleiotropy but have no evidence of directional pleiotropy
Unknown	Studies that cannot be classified as either “Evidence of causality” or “Likely noncausal”

Abbreviation: PI: prediction interval.