Case mix, outcomes and comparison of risk prediction models for admissions to adult, general and specialist critical care units for head injury: a secondary analysis of the ICNARC Case Mix Programme Database

Table 2 Measures of model calibration and discrimination in all admissions eligible for each model

Model	APACHE II	APACHE III	SAPS II	MPM II	ICNARC
Eligible admissions, n (percent)	8,344 (75.7)	9,021 (81.9)	8,220 (74.6)	7,267 (65.9)	10,285 (93.3)
AUC (95 percent CI)	0.73 (0.72, 0.75)	0.75 (0.74, 0.77)	0.81 (0.80, 0.82)	0.81 (0.79, 0.82)	0.82 (0.81, 0.83)
Hosmer-Lemeshow C*
χ²(10)^a	316	4542	162	99.5	94.6
p value	<0.001	<0.001	<0.001	<0.001	<0.001
Cox's calibration regression
Intercept (95 percent CI)	-0.23 (-0.29, -0.18)	0.44 (0.36, 0.52)	0.09 (0.03, 0.15)	0.27 (0.20, 0.34)	0.18 (0.12, 0.24)
Slope (95 percent CI)	0.66 (0.62, 0.70)	0.58 (0.55, 0.62)	0.86 (0.82, 0.90)	1.00 (0.94, 1.05)	0.97 (0.93, 1.01)
χ²(2)	262	2,045	74.8	84.8	66.3
p value	<0.001	<0.001	<0.001	<0.001	<0.001
Brier's score	0.187	0.193	0.164	0.168	0.155

^aNote that due to different sample sizes, the Hosmer-Lemeshow C*-statistic should not be directly compared between models. APACHE, Acute Physiology And Chronic Health Evaluation; AUC, area under the receiver operating characteristic curve; CI, confidence interval; ICNARC, Intensive Care National Audit & Research Centre; MPM, Mortality Probability Models; SAPS, Simplified Acute Physiology Score.

ISSN: 1364-8535