Statistical analysis
All the study results were presented as an odds ratio (OR) and 95% CI
to reach a consistent data. I2 was used to access the
heterogeneity in the meta-analysis. A random effect model was performed
if the I2 measurement was greater than 50%, and a
fixed effect model was performed if I2 was less than
50%. RevMan (Review Manager 5, version 5.3. Copenhagen: The Nordic
Cochrane Centre, The Cochrane Collaboration, 2014) was used in the
meta-analyses. The Newcastle-Ottawa scale was used to assess the quality
of the studies.