Assessment of comorbidity: a review

Eleven clinical comorbidity indices are reviewed with attention to the development of improved assessment of comorbid conditions. Elements that are critical to the indices are reviewed, including their applicability, their inclusiveness, their validation, their correlations with outcomes of interest, their inclusion of functional assessment, their inclusion of severity assessment, and their simplicity. Improved assessment of comorbidity will enable better understanding of the processes and outcomes of medical care.