Table 1.

Credibility Assessment Criteria for Meta-analyses of Observational Studies

Evidence Classification	Criteria
Convincing (Class I)	Associations with P < .000001; >1000 cases (or >20 000 participants for continuous outcomes) having the event of interest; the largest component study reporting a nominal, statistically significant result (P < .05); a 95% prediction interval that excluded the null; no large heterogeneity (I2 < 50%); no evidence of small-study effect (P > .10); no excess significance bias (P > .10).
Highly suggestive (Class II)	Associations with P < .000001; >1000 cases (or >20 000 participants for continuous outcomes) having the event of interest; the largest component study reporting a statistically significant result (P < .05).
Suggestive (Class III)	Associations with P < .001; >1000 cases (or >20 000 participants for continuous outcomes) having the event of interest.
Weak (Class IV)	Remaining statistically significant associations with P < .05.