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Statistical analysis

SZ Shuang Zhang
YL Yong Liu
XL Xiaohu Liu
TL Tianzhu Liu
PL Pengcheng Li
WM Wei Mei
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Statistical analyses were performed using SPSS 22.0 (IBM Corp., New York, NY, USA). As a diagnostic test, ROC curves were constructed to determine the sensitivity, specificity, and cut-off values of Td for predicting successful block. The optimal cut-off point was calculated by ROC curves with the maximal Youden index value (sensitivity+specificity-1). The area under the curve and the 95% confidence interval (CI) were reported as well.

Continuous variables were displayed as means (standard deviation) or medians (interquartile range [IQR] [25–75]), and discrete variables are expressed as numbers (n). The normally distributed data after Kolmogorov–Smirnov test were compared using the independent sample t-test, non–normal distributed data were analyzed using the Mann-Whitney U test. Categorical data were compared by χ2 test or Fisher’s exact. A P value of < 0.05 was considered statistically significant.

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