Association of Hormonal Contraceptive Use With Adverse Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials and Cohort Studies.

8 , 9 , 13 Associations from meta-analyses of cohort studies that were nominally significant (ie, P ≤ .05) were graded as having convincing (class 1), highly suggestive (class 2), suggestive (class 3), or weak (class 4) evidence based on the amount of evidence, statistical significance, heterogeneity, small-study effect, excess significance bias, prediction interval, and credibility ceiling test (details of classification criteria are provided in Table 1 ).

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