Development and validation of a prognostic nomogram model for Chinese patients with primary small cell carcinoma of the esophagus

Table 2 Concordance index of nomogram model and tumor node metastasis stage for overall survival prediction in the primary and validation cohorts

Variable	Primary cohort		Validation cohort
	C-index (95%CI)	P value	C-index (95%CI)	P value
Nomogram model	0.659 (0.607-0.712)	0.033	0.700 (0.622-0.778)	0.041
7th TNM staging	0.591 (0.517-0.666)		0.605 (0.490-0.721)

C-index: Concordance index; CI: Confidence interval; TNM: Tumor node metastasis.