Case mix, outcome and activity for obstetric admissions to adult, general critical care units: a secondary analysis of the ICNARC Case Mix Programme Database

Table 5 Measures of discrimination and calibration for APACHE II in obstetric and non-obstetric admissions

	All obstetric admissions (n = 1565)	Direct obstetric admissions (n = 1216)	Indirect or coincidental obstetric admissions (n = 349)	Female nonobstetric admissions aged 16–50 years (n = 18,450)
Discrimination (AUC [95% CI])
APACHE II score^a	0.839 (0.820 to 0.857)	0.819 (0.795 to 0.840)	0.839 (0.797 to 0.876)	0.812 (0.807 to 0.818)
APACHE II probability^a	0.810 (0.790 to 0.829)	0.737 (0.711 to 0.761)	0.806 (0.760 to 0.845)	0.855 (0.850 to 0.860)
Calibration
Mortality ratio (95% CI)	0.245 (0.167 to 0.346)	0.214 (0.120 to 0.352)	0.282 (0.163 to 0.453)	0.907 (0.878 to 0.937)
Hosmer–Lemeshow
C statistic (P value)	166 (< 0.001)	101 (<0.001)	47 (<0.001)	69 (<0.001)
Cox's regression calibration
Slope (95% CI)	0.728 (0.491 to 0.966)	0.570 (0.277 to 0.863)	0.937 (0.509 to 1.37)	1.05 (1.01 to 1.08)
Intercept (95% CI)	-2.09 (-2.60 to -1.59)	-2.57 (-3.39 to -1.76)	-1.69 (-2.33 to -1.05)	-0.120 (-0.179 to -0.061)
χ²₍₂₎ (P value)^a	140 (<0.001)	87 (<0.001)	55 (<0.001)	57 (<0.001)

^aχ² statistic with two degrees of freedom (and associated P value) from a likelihood ratio test of slope 1 and intercept 0 in Cox's regression calibration model. APACHE, Acute Physiology and Chronic Health Evaluation; AUC, area under the receiver operating characteristic curve; CI, confidence interval.