Psychometric and Utility-Based Measures of Health Status of Asthmatic Patients with Different Disease Control Level

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Abstract
Objective: To explore the relationship between asthma control level and healthrelated QOL (HR-QOL), and to understand the role of various psychometric and utility-based methods in studying this relationship. Methods: Two hundred and twenty-eight consecutive adult outpatients and inpatients at four sites participated in the study. Physicians identified the level of disease control according to the Global Initiative for Asthma (GINA) classification system. Patients filled in three different HR-QOL questionnaires (EuroQol 5-D [EQ-5D], Short-Form 36-item health survey [SF-36], and St George’s Respiratory Questionnaire [SGRQ]) and a direct time trade-off question. The Short Form- 6D (SF-6D) was used to derive utility values from SF-36 data. Results: All patient-reported evaluation methods could discriminate between patients with different disease control levels, and both generic and diseasespecific instruments strongly correlated to each other. The magnitude of differences in HR-QOL between groups with different disease control levels was clinically meaningful. All three HR-QOL measures reflected a relationship between disease control level and HR-QOL, but the actual pattern of the relationship depended on the instrument used. Utilities gained from the EQ-5D index, compared with the SF-6D index, had higher values in the patient group with the best disease control and lower values in the patient group with poor disease control. Conclusions: When choosing an instrument to measure the health status of asthmatic patients in clinical studies, the severity range of the study population should be considered. Researchers might prefer to use the EQ-5D in asthma patients with severe disease or poor disease control and the SF-6D in patients with mild disease or good disease control.