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.