Statistical Analysis of Continuous and Categorical Variables

All data were analyzed by SPSS Statistics software version 25.0 (IBM, Armonk, NY, USA), MedCalc software version 18.2.1 (MedCalc Software bvba, Ostend, Belgium), Empower (R) (www.empowerstats.com (accessed on 10 September 2020), X&Y Solutions, Inc., Boston, MA, USA) and R software (http://www.R-project.org (accessed on 10 September 2020)). Shapiro–Wilk tests were used to determine whether the continuous variables followed a normal distribution. The continuous variables conforming to a normal distribution were expressed as the mean ± standard deviation (SD), while those with a non-normal distribution were expressed as the median (interquartile range [IQR]). The Mann–Whitney U test was used to test the differences between the continuous variables, and the chi-square test was used to compare the differences between the categorical variables. DeLong’s test was used to compare the AUC values of the different prediction models [22 (link),25 (link)]. A p < 0.05 was considered to be a significant difference.