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UBC Theses and Dissertations

Longitudinal studies of disease progression, health care costs and health-related quality of life in patients with asthma Chen, Wenjia


This thesis examines the burden of asthma and its determinants though a series of longitudinal observational studies. Objectives: 1) To quantify the natural history of severe asthma and the impact of early risk factors; 2) To examine the influence of socioeconomic status (SES) on excess direct medical costs of moderate-to-severe asthma and guideline-based asthma care; 3) To estimate excess costs of asthma and the economic implications of comorbidities; 4) To assess the joint influences of asthma control and comorbidity on health-related quality of life. Methods: For the first three objectives, administrative health data (for the period of 1997-2013) were obtained from British Columbia (BC) Ministry of Health, and for the last objective data were obtained from the Economic Burden of Asthma (EBA) study in BC. Various models for longitudinal data were applied for each objective. Findings: 1) Most patients (83%) with incident severe asthma transitioned to milder states after 10 years. Low SES and comorbidity at disease onset led to worse long-term prognosis. 2) Across both individual- and neighborhood-levels, there was evidence that low-SES asthma patients and/or their care providers did not follow guideline-based asthma care and subsequently incurred substantially greater excess costs of asthma. 3) Excess costs in patients with asthma were $1187/year (95%CI $1130─$1243) overall, with comorbidity-attributable costs five times higher than asthma-attributable costs, all of which greatly increased with age. 4) Changes in asthma control had a greater effect on disease-specific (AQ5D) than generic (EQ5D) utilities, whereas changes in comorbidity burden had a larger impact on EQ5D than AQ5D utilities. Conclusions: With several novel methodology techniques, this thesis provided evidence for the first-time on the long-term trajectory and burden of asthma. Projection of cost and effectiveness of decisions and policies in asthma care requires a robust understanding of the natural history of asthma, effect of risk factors on this trajectory, and estimates of costs and health-related quality of life associated with asthma. This thesis provides new evidence on all such parameters. These findings have direct relevance to estimating cost-effectiveness of health technologies in asthma and can result in more informed decision-making in health policy and clinical practice.

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