Eligibility Criteria
For inclusion in analysis, studies must meet the following criteria: (1)
full-text published in English; (2) reported the odds ratio (OR),
relative risk (RR), or hazard ratio (HR), with 95% confidence interval
(95%CI), or adequate data to calculate these measures; (3) conducted
primarily in children (<18 years of age); (4) sample size of
at least 100. We excluded meta-analyses, review articles and case
reports. Two reviewers (J.X. and W.L.) screened the titles and
abstracts, and then assessed the full-text independently.