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An evaluation of patients’ preferences and health-related quality of life in asthma McTaggart-Cowan, Helen Ming

Abstract

Objectives: The objectives of this thesis were i) to quantify patients’ preferences for asthma treatments using a discrete choice experiment (DCE), ii) to evaluate the socioeconomic status (SES) impacts on these preferences, and iii) to assess the construct validity of three preference-based instruments (Health Utility Index Mark 3, EuroQol, and Short Form 6D). Methods: One hundred fifty-seven asthma patients between 19-49 years of age residing in metropolitan Vancouver, British Columbia participated in this cross-sectional study. The patients responded to three preference-based instruments, two disease-specific instruments (standardized version of the Asthma Quality of Life Questionnaire and Asthma Control Questionnaire (ACQ)), and a DCE. The DCE was designed to measure preferences for treatment benefit (symptom-free days (SFDs)), potential risks (oral thrush and tremor/heart palpitation), ease of use (frequency of daily administration and number of inhalers required), and cost. Information regarding the patient’s SES, pulmonary function, asthma medication use, and self-reported asthma control were also obtained. Results: Relationships between the relative preferences and all treatment attributes were generally in the hypothesized directions. Specifically, the patients were willing to pay an additional $14 per month to receive one extra SFD. Patients were willing to pay $26, $79, and $112 to avoid one, two, and three episodes of oral thrush, respectively, and were willing to forego 1.8, 5.5, 7.8 monthly SFDs to avoid one, two, and three episodes of oral thrush, respectively. Annual income and education level affected treatment preferences. Furthermore, the preference-based instruments were able to discriminate across levels of asthma control using the ACQ; however, there was a lack of discrimination between HRQL and asthma control using subjective measures, such as magnitude of short-acting β-agonist use and self-reported control status. Conclusions: The DCE results revealed that patients preferred treatments with more SFDs but they were willing to forego symptom relief to avoid greater frequencies of adverse events. The results demonstrated the construct validity of the preference-based instruments such that they were able to discriminate across the ACQ scores, providing evidence that preference-based instruments could detect minimal changes in asthma states.

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