Statistical analysis
SPSS17.0 software (SPSS IBM Inc., Chicago, IL, US) was used for statistical analysis. Measurement data are here presented as mean ± standard deviation (x̅ ± s). Normally distributed measurement data were compared using paired t-test. Non-normally distributed measurement data were compared using signed rank sum test of paired data, and comparison of the count data was performed using chi-square test. Correlation analysis was performed using logistic regression analysis. P< 0.05 was considered statistically significant.