2.4 Statistical analysis
The Chi-square test or Fisher’s exact test was used to analyze categorical variables, and t-test was used to analyze continuous variables. All statistical tests were two-sided, and a p value of less than 0.05 indicated statistical significance. The odds ratio (OR) and 95% confidence interval (CI) were also calculated. Statistical analyses were performed with SPSS 20.0 software (SPSS, Chicago, IL, http:// www. spss.com).