Objective: To explore the constructs underlying a self-report assessment of multimorbidity.
Study design and setting: We conducted a cross-sectional survey of 352 HMO members aged 65 years or more with, at a minimum, diabetes, depression, and osteoarthritis. We assessed self-reported 'disease burden' (a severity-adjusted count of conditions) as a function of biopsychosocial factors, two data-based comorbidity indices, and demographic variables.
Results: In multivariate regression, age, 'compound effects of conditions' (treatments and symptoms interfering with each other), self-efficacy, financial constraints, and physical functioning were significantly (p<or=0.05) associated with disease burden. An ICD-9-based morbidity index did not significantly contribute to disease burden, and a pharmacy-data-based morbidity index was minimally significant.
Conclusion: This measure of self-reported disease burden represents an amalgamation of functional capabilities, social considerations, and medical conditions that are not captured by two administrative data-based measures of morbidity. This suggests that (a) self-reported descriptions of multimorbidity incorporate biopsychosocial constructs that reflect the perceived burden of multimorbidity, (b) a simple count of diagnoses should be supplemented by an assessment of activity limitations imposed by these conditions, and (c) choice of the morbidity measurement instrument should be based on the outcome of interest rather than on the most convenient method of measurement.