Pathways and Protective Factors: Modelling the Effect of Chronic Conditions on Quality of Life in Midlife and Older Irish Adults
Background: Quality of life (QoL) outcomes are increasingly important as a target for healthcare intervention and for measuring healthcare effectiveness. However, the effect of physical health on QoL at older ages is poorly understood. The aim of this thesis was to empirically test an explanatory model of the relationship between chronic conditions and QoL in older people in Ireland.
Methods: This is a cross-sectional and longitudinal cohort study, using data from the Irish Longitudinal Study of Ageing (TILDA), a general-population sample of community-dwelling adults aged 50+ in the Republic of Ireland (n=8,175). Exploratory and confirmatory factor analysis was used to evaluate and revise the CASP-19 measure of QoL. Structural equation modelling was used to test a model of the pathway between chronic conditions and QoL, via disability and affective wellbeing. Conditional change linear regression was used to evaluate longitudinal effects along this pathway, and to examine how these longitudinal effects were modified by personal characteristics (e.g., personality) and environmental factors (e.g., social support).
Results: A 12-item version of CASP-19 was developed, comprising two dimensions: control/autonomy and self-realisation/pleasure. The cross-sectional effect of chronic conditions on both QoL dimensions was mediated by physical impairment and affective wellbeing. Partner support reduced the effect of physical impairment on control/autonomy and religiosity reduced the effect of physical impairment on self-realisation/pleasure. Self-realisation/pleasure was less responsive to variation and change in physical health relative to control/autonomy.
Conclusion: The effect of chronic conditions on QoL in later life depends on the level of disability, the availability of environmental supports, and personal characteristics. Models of healthcare which focus on patient-specific goals, circumstances and health needs, rather than specific conditions and disease processes, may be more effective for improving QoL outcomes in chronic disease. Control/autonomy emerged as a useful indicator of QoL which is responsive to variation in physical health.