Objective: Though health-related quality of life (HRQoL) is now commonly measured as an outcome in clinical trials, the relationships between its components remain unclear. The relation of physical symptoms, physical function, and psychological symptoms to each other and to overall quality of life is of special interest.
Method: Cross-sectional data from 5,279 community-dwelling elders who participated in the Groningen Longitudinal Aging Study were analyzed using structural equation modeling techniques. Three models were examined. One "Linear" model included: number of chronic medical conditions, physical symptoms, physical functioning, activity interference, social function, perceived health and overall quality of life in a simple linear progression. Another 'non-linear' model included these variables, but allowed effects between non-adjacent variables. A third 'non-linear' model included these variables plus anxiety and depressive symptoms.
Results: The Linear Model did not satisfactorily account for the observed data [X2(15df) = 2946.96], so the saturated Non-Linear Model, incorporating paths between non-adjacent components, is described. When anxiety and depressive symptoms were added to this Non-Linear Model, they fit best in a position mediating the relation between perceived health and overall quality of life [X2(5df) = 136.78].
Conclusions: Overall quality of life appears to be related to symptom status as directly as it is related to functional status. Anxiety and depressive symptoms appear to mediate the relation between general health perceptions and overall quality of life. Quality of life measures should therefore include assessments of physical and psychological symptom severity as well as functional status if they are to truly reflect what matters to patients. The disability-adjusted life year (DALY) measure used by the WHO may inadequately reflect the effect of symptoms on patient's quality of life.