External validation of a Cox prognostic model: principles and methods

Table 3 Some methods for external validation and the level of information about the derivation study they require

	Method	Aspect	Information
			L1	L2	L3
1	Regression on PI in validation data	D, F	$✓$	$✓$	$✓$
2	Check model misspecification/fit	F	$✓$	$✓$	$✓$
3	Measures of discrimination	D	$✓$	$✓$	$✓$
4	Kaplan-Meier curves for risk groups	D, C	×	$✓$	$✓$
5	Logrank/Cox tests between risk groups	D	×	$✓$	$✓$
6	Hazard ratios across risk groups	D	×	$✓$	$✓$
7	Calibration	C	×	×	$✓$

L1, L2 and L3 denote increasing amounts of information (see text). Key to Aspect: D, discrimination; C, calibration; F, model fit.