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.