2.4 Statistical analysis
The normality of the variables was tested with the Shapiro-Wilk, and
Skewness/Kurtosis tests. Continuous variables are expressed as the mean
and standard deviation or median with the 25th to
75th percentile interval. Univariable analysis was
applied with appropriate test (Fisher’s exact tests or Chi squared
tests), depending on the observed frequency. A paired t-test was used
for the difference between two variables for the same subject. Possible
risk factors for a poor outcome with p< 0.25 on Cox
univariable analysis were assessed by competing risk analysis using the
Stata software package (version 14.1; Stata Corp, Texas, USA). A p-value
< 0.05 was considered to indicate statistical significance.
Actuarial survival, freedom from reoperation and reintervention were
estimated by the Kaplan-Meier method.