Statistical analyses
Descriptive analysis was conducted to evaluate the pattern of PAG problems overall and by age, year, and region. The differences in those patterns across age, year and region were evaluated using χ2 test of proportions. All analyses were conducted using SAS software, version 9·3 (SAS Institute Inc., Cary, NC).
The meta-analysis was conducted with Stata 16·0 (Stata Corp, College Station, TX, USA). For each study in the systematic review, we calculated the weighted average percentage of each article that met our inclusion criteria by taking disease species as subgroup. Because not all of the articles included in the meta-analysis had all disease classifications, the disease proportion was weighted to 100% for final analysis. By using the I2 statistic to assess heterogeneity between studies, summarized effect size (ES) (95% CI) was derived.