2.4 Statistical Analysis
The data were analyzed by using the SPSS package program (SPSS 23, IBM
Corp. Released 2015. IBM SPSS Statistics for Windows, Version 23.0.
Armonk, NY, USA). The suitability of variables to normal distribution
was determined using the Kolmogorov–Smirnov test. Normally distributed
continuous variables were expressed as mean ± standard deviation, while
those without normal distribution were expressed as median (25%–75%
percentile). Categorical variables were expressed in numbers and
percent. Student t-test was performed for normally distributed
continuous variables, while Mann–Whitney U-test was performed for those
without normal distribution. Pearson’s chi-square and Fisher’s exact
tests were used to evaluate categorical variables. For correlation
analysis, the Pearson correlation coefficient was used when the
preconditions of the parametric test were met, and the Spearman
correlation coefficient was used when the preconditions were not met. A
P value < 0.005 was considered to reflect statistical
significance.