Statistical analysis
Continuous variables are expressed as the mean ± SD, and the significant
differences were analyzed with a Student’s t test. Categorical data are
expressed as the number and percentages, and were compared using an
χ2 test or Fisher’s exact test. Univariate and
multivariate Cox proportional hazards regression analyses were performed
on candidate variables to predict the dichotomous outcome. The variables
with a P < 0.1 in the univariate analysis were input into the
multivariate analysis. Survival curves were calculated using the
Kaplan–Meier method and compared with the Log Rank test. A probability
value of < 0.05 was deemed significant. Statistical analyses
were conducted using the EZR software (Saitama Medical Center, Jichi
Medical University, Saitama, Japan), which is a graphical user interface
for R (The R Foundation for Statistical Computing, Vienna, Austria).