Spss program for windows version 21

All statistical analyses were performed using SPSS program for Windows version 21.0 (SPSS, Chicago, IL, USA). The Shapiro-Wilk test was used to check the data for normality. Comparisons between the groups were performed using the Student t test for continuous normal distribution data and the Mann-Whitney U test for ordinal categorical and non-normal distribution data. Comparisons within the groups between the preoperative and postoperative data were performed using a paired t-test for continuous normal distribution data and a Wilcoxon signed-rank test for ordinal categorical and non-normal distribution data. A Pearson chi-square test was used for nominal categorical data. The level of significance was set at p ≤ 0.05. A post-hoc power analysis was performed using G*Power version 3.1.2 to assess the validity of the sample size based on the comparison of postoperative 1 year YBT composite score LSI.

Data are presented as means ± SEM. Equality of variances between groups was assessed by Levene’s test. When homogeneity of variances was assumed, one-way ANOVA was used to determine the significance of the different parameters between groups. If there was a significant difference, a Bonferroni test was used to determine where the difference lay and to correct for multiple testing. When homogeneity of variances was not assumed, data were log transformed. Linear relationships between key variables were tested using Pearson's correlation coefficients. Threshold of significance was set at P<0.05. The analysis was performed using the SPSS program for Windows version 21.0 (SPSS, Chicago, IL, USA).