Statistical analysis
Continuous variables (e.g., age) were given as mean±SD, and were analyzed with t tests if they conformed to a normal distribution and Mann-Whitney U tests if not. Comparisons between more than 2 groups made with one-way analysis of variance. Categorical variables (e.g., gender) were compared using the χ2 test or the Fisher exact test. P <0.05 was considered significant. All analyses were performed using JMP Pro statistical software (version 10, SAS Inc, Cary, NC) and Microsoft Excel.