Statistical basis and clinical applications of severity of illness scoring systems in the intensive care unit

Tremendous growth has occurred in the development of new severity of illness scoring systems in predicting outcomes in the intensive care unit. Many of these models are being applied in international settings. Severity-of-illness models have been used not only for patient outcomes but also for evaluating resource utilization patterns. Physicians should have a basic understanding of the statistical foundations that form the essence of these models so that these models can be applied appropriately and fully to address the patient care, policy, and ethical issues that frequently surround decision making in the intensive care unit.