Statistical Analysis

The summary of the statistical analyses includes the values of the mean and standard deviation (SD) of frequencies and percentages. Missing data were not defaulted to negative, and denominators reflect only reported cases. Univariate associations between the 2 groups for nominal variables were compared using the Pearson χ² test or Fisher's exact test, and the 2-tailed Student t test was used to evaluate continuous variables. Data analysis was performed using Statistical Package for Social Sciences (SPSS) v. 17.0 for Windows (SPSS Institute, Chicago). P < 0.05 was considered statistically significant.