Statistical analysis
Descriptive statistics were calculated for the patients’ characteristics and SBE parameters, and are presented as medians, means, and ranges. Continuous variables were expressed as mean (standard deviation) or median (range). Categorical variables were presented as numbers and percentages or rates. Differences in numerical variables were analyzed by the Student’s t-test, or the Mann-Whitney U test. While differences in categorical variables were analyzed by the χ2 test, or Fisher’s exact test. A two-sided P value of less than 0.05 was considered statistically significant. All the statistical analyses were performed using SPSS 21.0 (IBM, Armonk, USA).