Table 4. Predictive accuracy of age in continuous type and categorical type (6 groups and 3 groups).

Age	Training set			Internal validation set			External validation set
	C-index	AIC		C-index	AIC		C-index	AIC
Continuous	0.7539	7,773.2		0.7359	8,695.0		0.7426	1,794.1
Categorical (6 groups)	0.7532	7,777.9		0.7350	8,712.9		0.7391	1,802.8
Categorical (3 groups)	0.7531	7,769.7		0.7344	8,714.3		0.7431	1,772.1

C-index, Harrell’s concordance index; AIC, Akaike’s Information Criterion.