Severity-of-illness scores can be used to better understand the clinical performance and resource allocation of providers caring for populations, to provide guidance for quality improvement activities, and to adjust for case mix differences in clinical research and comparative benchmarking.

Specific severity-of-illness scoring systems for critically ill children have been available for decades and perform well at the group level in predicting outcomes.

Epidemiologic and statistical principles are fundamental to the design, validation, and application of severity-of-illness scoring systems.

Standardized ratios can be used for outcomes of mortality, length of stay, infection rates, and other quality outcomes to determine statistically significant differences of actual performance from expected.

Standardized ratios are created by dividing the observed outcomes rates by the expected. A value <1 indicates performance that is better than expected, whereas a value >1 indicates performance that is worse than expected.

Newly developed severity-of-illness scoring systems require validation to assure that they accurately predict and discriminate on the outcome of interest in other populations.

As medical care changes, scoring systems require recalibration to assure that they remain contemporary indicators for adjusting case mix.