Deriving utility scores for co-morbid conditions: a test of the multiplicative model for combining individual condition
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BioMed Central
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Deriving utility scores for co-morbid conditions: a test of the multiplicative model for combining individual condition scores William Flanagan, Cameron N McIntosh*, Christel Le Petit and JeanMarie Berthelot Address: Health Analysis and Measurement Group, Statistics Canada, R.H. Coats Building, Ottawa, Ontario, K1A 0T6, Canada Email: William Flanagan - [email protected]; Cameron N McIntosh* - [email protected]; Christel Le Petit - [email protected]; Jean-Marie Berthelot - [email protected] * Corresponding author
Published: 31 October 2006 Population Health Metrics 2006, 4:13
doi:10.1186/1478-7954-4-13
Received: 19 May 2006 Accepted: 31 October 2006
This article is available from: http://www.pophealthmetrics.com/content/4/1/13 © 2006 Flanagan et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: The co-morbidity of health conditions is becoming a significant health issue, particularly as populations age, and presents important methodological challenges for population health research. For example, the calculation of summary measures of population health (SMPH) can be compromised if comorbidity is not taken into account. One popular co-morbidity adjustment used in SMPH computations relies on a straightforward multiplicative combination of the severity weights for the individual conditions involved. While the convenience and simplicity of the multiplicative model are attractive, its appropriateness has yet to be formally tested. The primary objective of the current study was therefore to examine the empirical evidence in support of this approach. Methods: The present study drew on information on the prevalence of chronic conditions and a utilitybased measure of health-related quality of life (HRQoL), namely the Health Utilities Index Mark 3 (HUI3), available from Cycle 1.1 of the Canadian Community Health Survey (CCHS; 2000–01). Average HUI3 scores were computed for both single and co-morbid conditions, and were also purified by statistically removing the loss of functional health due to health problems other than the chronic conditions reported. The co-morbidity rule was specified as a multiplicative combination of the purified average observed HUI3 utility scores for the individual conditions involved, with the addition of a synergy coefficient s for capturing any interaction between the conditions not explained by the product of their utilities. The fit of the model to the purified average observed utilities for the co-morbid conditions was optimized using ordinary least squares regression to estimate s. Replicability of the results was assessed by applying the method to triple co-morbidities from the CCHS cycle 1.1 database, as well as to double and triple co-morbidities fr
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