Statistical analysis

Categorical variables were compared using the Fisher exact test or the chi-square exact test, as appropriate. For differences between continuous variables, the independent t-test was used. In order to compare the five models, we used repeated-measure one-way analysis of variance with a post hoc Bonferroni correction. All analyses were performed using IBM SPSS ver. 20.0 (IBM Corp., Armonk, NY, USA). Double-angle plots with 95% confidence ellipses were obtained using Sigmaplot ver. 12.5 (Systat Software Inc., San Jose, CA, USA) and R ver. 3.3.1 (R Foundation, Vienna, Austria). A p-value <0.05 was considered statistically significant.