Heterogeneity was evaluated using Cochran Q and I2 statistics, which is reported as chi-square (χ2), P value and percentage. Heterogeneity is one of the main contents of the meta- analysis report. When P 0.10 and I2>50%, it indicates that there is significant heterogeneity between studies, and it is necessary to use a random effect model to combine OR and 95%CI. If not, we used fiXed effect model to analyze.