Table 3.
Model fit – comparison of the SAPS II, APACHE II and ICNARC models
| SAPS II model | APACHE II model | ICNARC model | |
|---|---|---|---|
| Eligible admissions, n (%) | 4,973 (64.6) | 6,212 (80.7) | 7,156 (93.1) |
| Observed deaths | 3,030 | 3,579 | 4,237 |
| Expected deaths | 2,675.2 | 3,538.5 | 3,393.3 |
| SMR (95% CI) | 1.13 (1.11 to 1.16) | 1.01 (0.99–1.03) | 1.25 (1.22 to 1.27) |
| AUROC (95% CI) | 0.74 (0.73 to 0.75) | 0.74 (0.73 to 0.76) | 0.79 (0.78 to 0.80) |
| Hosmer–Lemeshow Ca statistic | |||
| χ2(10) | 568.0 | 68.0 | 900.9 |
| P value | < 0.001 | < 0.001 | < 0.001 |
| Cox's calibration regression | |||
| Intercept (95% CI) | 0.44 (0.38 to 0.51) | 0.08 (0.02 to 0.14) | 0.62 (0.56 to 0.67) |
| Slope (95% CI) | 0.59 (0.54 to 0.63) | 0.80 (0.75 to 0.85) | 0.77 (0.73 to 0.81) |
| χ2(2) | 469.4 | 54.3 | 708.95 |
| P value | < 0.001 | < 0.001 | < 0.001 |
The Hosmer-Lemeshow test divides the data into ten groups and compares the observed mortality in these groups to the predicted mortality given by the model. The C statistic is a chi-squared statistic for testing the hypothesis of perfect calibration. A significant value for the C statistic indicates that calibration is not perfect.
APACHE II: Acute Physiology and Chronic Health Evaluation II; AUROC: area under the receiver operating characteristic curve; CI: confidence interval; ICNARC: Intensive Care National Audit and Research Centre; SAPS II: Simplified Acute Physiology Score II; SMR: standardised mortality ratio. a