These results indicate that our measure of self-reported disease burden represents a complex amalgamation of functional capabilities, social considerations, and medical conditions that are not captured by two 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 limitations imposed by these conditions, and c) choice of morbidity measurement instrument should be based on the outcome of interest rather than the most convenient method of measurement.
These findings are consistent with previous investigations that demonstrate that the incorporation of severity assessment improves the predictive validity of self-report morbidity measures, and that severity assessment is particularly important when morbidity is measured as part of investigations assessing functional or general health status outcomes.(5
) We expand on these findings to explore the constructs underlying self-report of conditions with associated severity assessment.
When respondents with multimorbidities in this investigation quantified their level of morbidity, they incorporated the effect of conditions on their level of physical functioning, reflected their level of confidence in managing their medical conditions (self-efficacy), and reflected the burden of financial constraints imposed by their multimorbidities. They also captured the concept that having discordant chronic conditions in which symptoms and/or treatments interfere with each other (‘compound effects of conditions’) adds to disease burden.
We were not surprised to find that respondents incorporated level of physical functioning into their assessment of their own disease burden—especially since the instrument was worded to capture how much their conditions “interfered with daily activities”. This concept would not be fully captured by either ICD-9 diagnoses, or morbidity assessments based on pharmacy data.
The significance of financial constraints in this model may reflect the particular burden of multimorbidity for seniors on fixed incomes (even in an insured HMO population) and is consistent with other suggestions that social constructs such as socioeconomic status affect the complexity of patient care.(32
) For example, the questions that inquired about financial constraints in the survey asked whether respondents had cut down on other purchases as a result of health care expenses and whether they were able to pay for all their health care needs and prescriptions. These concepts might be partially captured by a pharmacy-based index, but would not necessarily be captured by the ICD-9-based Quan index.
Self-efficacy is an important personal resource that can substantially affect successful self-care and health outcomes for persons with chronic conditions.(35
) The current self-report measure suggests that low self-efficacy may magnify limitations imposed by chronic conditions and that a higher burden of chronic conditions is independently associated with lower self-efficacy. This is particularly important given that interventions to improve self-efficacy in heterogeneous populations can result in improved health outcomes.(36
The final factor captured by disease burden is what we term ‘compound effects of conditions.’ This is the concept that, for certain coexisting conditions, symptoms and/or treatments interfere with each other. For respondents with these discordant conditions, their disease burden is more than the sum of the parts of their diagnoses. This concept is particularly difficult to capture using data-based morbidity assessments, which is an argument for including self-report as part of a complete assessment of health status in persons with multiple chronic conditions.
A complete description of health includes a range of perspectives from those that are completely subjective (such as the perception of pain) to those that are more objective (such as the observation of dementia).(38
) This disease burden instrument primarily measures aspects of health (and morbidity) that are subjective in nature: the perceived limitation due to a constellation of medical conditions (and the underlying equally subjective biopsychosocial constructs). Likewise, a complete description of health status can be described in terms of multiple outcomes. These include more ‘objective’ outcomes such as cost, as well as more ‘subjective’ outcomes such as quality of life. Although the two administrative data-based morbidity instruments that we used (Quan and CDS) did not contribute to our measure of disease burden, these measures have been extensively validated against other health outcomes such as utilization and cost of care.(17
) Choosing the correct instrument to assess morbidity burden for any outcome requires knowledge of the components captured by different measures. Often the richest assessment will result from incorporation of more than one morbidity measure.(39
) Choice of morbidity measurement instruments should be based on the outcomes of interest rather than simply on the most convenient methods for measurement. Furthermore, complete measurement of morbidity to reflect overall health status likely requires the use of self-report in addition to other measures.