Statistical methods:
Continuous, normally distributed variables are presented as mean ± SD
and compared using the Student’s t test. Ordinal and/or non-normally
distributed variables were compared using the Wilcoxon rank-sum test.
Normality was assessed using the Shapiro-Wilk test and visual inspection
of quantile-quantile (QQ) plots and skews. Categorical variables were
compared using the Chi-square test. All analyses were made using “R”
program language platform (version 3.5.3, 2019-03-11).