The Functional Comorbidity Index Is Useful to Predict Quality of Life

Abstract

Objectives:

Comorbidity indexes adjust for comorbidity confounding on a specific outcome, but no index is designed specifically for a quality of life (QOL) outcome. The Functional Comorbidity Index was previously designed to predict physical function-related QOL. The goals of this study: 1) Assess the Functional Comorbidity Index as a predictor of general QOL in sleep apnea patients (measured by SF-36 component scores); 2) Compare the ability to predict general QOL between the Functional Comorbidity Index and the widely used Charlson Comorbidity Index.

Methods:

Between 2004-2007 669 adults with sleep apnea were prospectively enrolled and data collected for the QOL outcome variables and the comorbidity indexes as independent variables. A random sample of 250 was analyzed with Spearman correlations between each index and QOL measures. Multivariate linear regression models calculated the ability to predict QOL (adjusted R2) adjusted for demographics and sleep apnea severity. Bootstrapping generated variances in the regression coefficients to test statistically for a clinically important (10%) difference between indexes.

Results:

Correlations of the Functional and Charlson Comorbidity Indexes with the mental component of QOL were -0.38 (P < 0.0001) and -0.07 (P = 0.2946), respectively. The Functional Comorbidity Index was clinically and statistically superior to the Charlson Comorbidity Index for predicting the mental component of QOL (adjusted R2 0.23 and 0.13, respectively, P < 0.001). Similar results were found for predicting the physical component of QOL.

Conclusions:

The Functional Comorbidity Index is useful to predict QOL and is a more robust predictor of QOL than the Charlson Comorbidity Index in sleep apnea patients.