Spss 22.0 package for windows

Kolmogorov-Smirnov test was used to determine the distribution of variables. Nonparametric tests were applied for the variables with no Gaussian distribution. Kruskal-Wallis test was used for effective differences among all groups. For comparing differences between groups in continuous variables with non-normal distribution Mann–Whitney-U tests were appropriate. Spearman correlation test was adequate to rank and measure the relationship between two continuous random variables. SPSS 22.0 package for Windows (SPSS Inc., Chicago, IL, USA) was applied for all statistical analyses. Differences were considered statistically significant at *P < 0.05, **P < 0.01 and ***P < 0.001.

All statistical analyses were performed with SPSS 22.0 package for Windows (SPSS Inc., Chicago, IL, USA). Continuous variables were tested for normality by the Kolmogorov–Smirnov test. Comparability between the three groups was analyzed using the Kruskal–Wallis test for non-normally distributed continuous variables or the ANOVA test for normally distributed continuous variables. Comparisons of categorical variables were performed using the Chi-square test for categorical variables. The Kaplan–Meier curve was performed to analyze the survival probability and compared using a two-sided log-rank test. Potential risk factors with a P value of < 0.1 in the univariate analysis were included in the multivariate Cox proportional hazard regression model with a forward stepwise procedure. Hazard ratio (HR) and 95% confidence interval (CI) were subsequently calculated. A two-sided P value of 0.05 was used as the threshold for statistical significance. GraphPad Prism 8.0 and Microsoft PowerPoint were used for graph drawing.