Statistical analysis
Statistical analysis was performed using the statistical package for
social sciences (SPSS) software version 16 (IBM Inc, Chicago, Il). The
Kolmogorov-Smirnov and Shapiro-Wilk tests were used to assess the
normality distribution of continuous data. If the number of cases was
larger than 30, the Kolmogorov-Smirnov test was used, while the
Shapiro-Wilk test was used for data of less than 30 subjects. Normally
distributed data were presented using mean and standard deviation (SD),
while non-normally distributed data were presented using median and
interquartile range (IQR). Comparison of normally distributed continuous
variables between groups was performed using one-way analysis of
variance (ANOVA) with Bonferroni post hoc test. Non-normally distributed
variables were compared between groups using the Kruskal-Wallis test and
Mann-Whitney test for comparing variables between two groups.