Searching for an improved clinical comorbidity index for use with ICD-9-CM administrative data

UMMS Affiliation

Department of Quantitative Health Sciences

Publication Date


Document Type



Aged; Comorbidity; Coronary Artery Bypass; Coronary Disease; Female; Hospital Mortality; Humans; Male; Middle Aged; Models, Statistical; Multivariate Analysis; Reproducibility of Results


Biostatistics | Epidemiology | Health Services Research


We studied approaches to comorbidity risk adjustment by comparing two ICD-9-CM adaptations (Deyo, Dartmouth-Manitoba) of the Charlson comorbidity index applied to Massachusetts coronary artery bypass surgery data. We also developed a new comorbidity index by assigning study-specific weights to the original Charlson comorbidity variables. The 2 ICD-9-CM coding adaptations assigned identical Charlson comorbidity scores to 90% of cases, and specific comorbidities were largely found in the same cases (kappa values of 0.72-1.0 for 15 of 16 comorbidities). Meanwhile, the study-specific comorbidity index identified a 10% subset of patients with 15% mortality, whereas the 5% highest-risk patients according to the Charlson index had only 8% mortality (p = 0.01). A model using the new index to predict mortality had better validated performance than a model based on the original Charlson index (c = 0.74 vs. 0.70). Thus, in our population, the ICD-9-CM adaptation used to create the Charlson score mattered little, but using study-specific weights with the Charlson variables substantially improved the power of these data to predict mortality.

DOI of Published Version



J Clin Epidemiol. 1996 Mar;49(3):273-8. Link to article on publisher's site

Journal/Book/Conference Title

Journal of clinical epidemiology

PubMed ID


Related Resources

Link to Article in PubMed