Performance of comorbidity scores to control for confounding in epidemiologic studies using claims data

Comorbidity is an important confounder in epidemiologic studies, The author s compared the predictive performance of comorbidity scores for use in epid emiologic research with administrative databases. Study participants were B ritish Columbia, Canada, residents aged greater than or equal to 65 years w ho received angiotensin-converting enzyme inhibitors or calcium channel blo ckers at least once during the observation period. Six scores were computed for all 141,161 participants during the baseline year (1995-1996). Endpoin ts were death and health care utilization during a 12-month follow-up (1996 -1997). Performance was measured by using the c statistic ranging from 0.5 for chance prediction of outcome to 1.0 for perfect prediction. In logistic regression models controlling for age and gender, four scores based on the International Classification of Diseases, Ninth Revision (ICD-9) generally performed better at predicting 1-year mortality (c = 0.771, c = 0.768, c = 0.745, c = 0.745) than medication-based Chronic Disease Score (CDS)-1 and CDS-2 (c = 0.738, c = 0.718). Number of distinct medications used was the b est predictor of future physician visits (R-2 = 0.121) and expenditures (R- 2 = 0.128) and a good predictor of mortality (c = 0.745). Combining ICD-9 a nd medication-based scores improved the c statistics (1.7% and 6.2%, respec tively) for predicting mortality Generalizability of results may be limited to an elderly, predominantly White population with equal access to state-f unded health care.