Table 3.

Performance measures of survival models, with the cutoff value for predicted probability = 10%,* for the 2003 sample

Measure	Sensitivity†			Specificity†			PPV†			NPV†
	n	%	(se)	n	%	(se)	n	%	(se)	n	%	(se)
3-month survival	2974/2984	99.7	(0.1)	68/2639	2.6	(0.3)	2974/5545	53.6	(0.7)	68/78	87.2	(3.8)
6-month survival	2329/2360	98.7	(0.2)	207/3263	6.3	(0.4)	2329/5385	43.3	(0.7)	207/238	87.0	(2.2)
1-year survival	1762/1823	96.7	(0.4)	543/3800	14.3	(0.6)	1762/5019	35.1	(0.7)	543/604	89.9	(1.2)
2-year survival	1235/1329	92.9	(0.7)	1099/4294	25.6	(0.7)	1235/4430	27.9	(0.7)	1099/1193	92.1	(0.8)

PPV: positive predictive value

NPV: negative predictive value

se: standard error

* As 10% was chosen as the cutoff value for predicted probability, patients with a predicted probability of survival < 10% were classified as a group that would die before the end of observation period, and those with a predicted probability of survival > = 10% were classified as a group that would survive the whole observation period. By comparison of predicted outcomes with actual outcomes, we further calculated the four measures for reflecting the quality of predictions in different perspectives.

^† The formulae for these measures are below:

sensitivity = (the number of patients with a predicted probability of survival > = 10%)/(the number of patients who actually survive the whole observation period);

specificity = (the number of patients with a predicted probability of survival < 10%)/(the number of patients who actually died before the end of observation period);

PPV = (the number of patients who actually survive the whole observation period)/(the number of patients with a predicted probability of survival > = 10%);

NPV = (the number of patients who actually died before the end of observation period)/(the number of patients with a predicted probability of survival < 10%).