The data of qualitative variables will be expressed as absolute values and relative frequencies. The data of quantitative variables will be shown as mean ± standard deviation should be demonstrated normal distribution or median with interquartile range otherwise. Categorical variables will be compared using X ^ 2 or Fisher's exact test. Continuous variables will be compared using the Student's t-test or the Mann-Whitney U test. Statistical analysis will be conducted using SPSS version 15.0 (SPSS Inc, Chicago, Illinois, USA).