Statistical analysis
The statistical analysis was performed using the SPSS statistical software system (SPSS Inc., Chicago, IL; version 22.0). Data are represented as means and standard deviations. Nonparametric tests were used for comparisons across groups for pretreatment and posttreatment data that were not normally distributed. Intragroup comparisons were performed using paired t tests or Wilcoxon rank-sum tests. Two-tailed 