4. Statistical analysis
The study data were subjected to  statistical analysis using the SPSS version 20.0 (SPSS Inc, Chicago, IL). All data were expressed as numbers, percentiles, mean, median, and standard deviation (SD). Student t test was used for univariate analysis of the difference between groups. Mann-Whitney U test was performed as the non-parametric test. The receiving operating characteristic (ROC) curve and the value of area under the curve (AUC) were used to analyze the accuracy of different parameters to predict AL and the best cut-off point was selected. p<0.05 was considered statistically significant.