3. Statistical Analysis
The patients' data were analyzed by software SPSS for Windows release 13. The association among the HLA alleles, different clinical features, and gender was investigated using Fisher's exact test and Pearson's corrected chi-square test. P  values ≤ 0.05 were considered significant after correction for the number of alleles with a frequency higher than 5% (nonrare allele). The delta method was used to calculate the confidence interval (variance) of the prevalence ratio (PR).