Adult risk adjustment: To develop and validate the optimum method for risk adjustment of hospital mortality for adult intensive care in the UK


Using statistical techniques, it is possible to build models that predict how likely a patient is to experience a particular outcome or condition. These risk models (or prognostic models) can be used to ‘risk adjust’ outcomes by taking into account severity of illness of patients to make fairer comparisons between health care providers.

At the time of this study, and since the validation of the APACHE II method in the UK which led to the establishment of ICNARC, a number of new methods had been developed outside of the UK to risk adjust hospital mortality in adult intensive care. 

The aim of this study was to identify the best risk adjustment method to use for hospital mortality in adult intensive care.


The study used data from the Case Mix Programme for:

  • Assessing and comparing the current methods
  • Optimising the performance of the current methods (‘recalibrating’ the models) and comparing the methods following recalibration
  • Developing and assessing new a new method and comparing it with the current methods.


Risk prediction models developed in another country require validation and recalibration before being used to provide risk-adjusted outcomes within a new country setting. Regular reassessment is beneficial to ensure performance is maintained.   


The new model (ICNARC model) performed better in a UK setting than existing risk prediction models, even following recalibration of these models.

Evaluating existing models

The ICNARC model

Who led the study? 

Professor Kathy Rowan, ICNARC 

The study was funded by the Medical Research Council (Project: G9813469)


Harrison DA, Rowan KM. Outcome prediction in critical care: the ICNARC model. Curr Opin Crit Care 2008; 14(5):506-12.

Harrison DA, Parry GJ, Rowan K. Risk prediction models: recalibration. Crit Care Med 2007; 35(1):326-7.

Harrison DA, Parry GJ, Carpenter JR, Short A, Rowan K. A new risk prediction model for critical care: the Intensive Care National Audit & Research Centre (ICNARC) model. Crit Care Med 2007; 35(4):1091-8.

Harrison DA, Brady AR, Parry GJ, Carpenter JR, Rowan K. Recalibration of risk prediction models in a large multicenter cohort of admissions to adult, general critical care units in the United Kingdom. Crit Care Med 2006; 34(5):1378-88.

Wunsch H, Brady AR, Rowan K. Impact of exclusion criteria on case mix, outcome, and length of stay for the severity of disease scoring methods in common use in critical care. J Crit Care 2004; 19(2):67-74.

Mourouga P, Goldfrad C, Rowan K. Does it fit? Is it good? Assessment of scoring systems. Curr Opin Crit Care 2000; 6(3):176-80.