Problems in determining occurrence rates of multimorbidity

This article describes methodological decisions that have to be made when s tudying multiple pathology and presents appropriate analytical techniques. The main question of this article is: how can comorbidity and multimorbidit y be operationalized with respect to the number and type of diseases studie d. and which analytic approaches are available for the evaluation of multip le pathology? Choices regarding the number and type of diseases studied hav e great impact on the observed incidence and prevalence rates of comorbidit y and multimorbidity. These rates are largely dependent on age. sex, and ot her determinants. In addition to crude descriptive measures, odds ratios an d relative risks can be used to study comorbidity. whereas multimorbidity c an be studied using observed/expected ratios. While basic analyses of comor bidity can be performed using standard statistical packages, two additional programs were developed for the analysis of the distribution of multimorbi dity and statistically unexpected comorbidity, respectively. As some analys es are addressing multi-comparisons, external validity testing is recommend ed. (C) 2001 Elsevier Science Inc. All rights reserved.