Risk of bias assessment

Two researchers (WL and JL) independently assessed the potential bias of the studies. All discrepancies in quality ratings were discussed with a third researcher (QL). Based on the results of the pre-test, we used the Joanna Briggs Institute Prevalence Critical Appraisal Tool (7), which is specifically used for systematic reviews of prevalence studies. Sample representativeness, sampling method, sample size, study subjects and setting, coverage of the identified sample, using of standardized criteria for the measurement, reliability of the measurement, appropriateness of the statistical analysis, confounding factors/subgroups/differences, and objectiveness of the criteria of subpopulations were evaluated in all included studies.