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Abstract
Three methods have been developed to measure health-related quality of life (HRQoL) expressed as a single value: the global rating scale, the total score obtained from disease-specific instruments, and the preference-based utility index. We compared these different single HRQoL measurements in patients with asthma and chronic obstructive pulmonary disease (COPD). We recruited 167 patients with asthma and 161 patients with COPD. The global rating HRQoL was assessed by the Hyland scale. The total HRQoL was assessed by the Living With Asthma Questionnaire in asthma and the St. George's Respiratory Questionnaire in COPD. The Quality of Well-being (QWB) scale was used for the utility measurement derived from the Medical Outcome Study Short-form 36. The inter-relationships between these three HRQoL values were weak to moderate in asthma and moderate in COPD. In asthma, the Hyland scale was weakly correlated with the total HRQoL (Spearman's rank correlation coefficients [Rs] = −0.20) and moderately with the QWB score (Rs = −0.43). In the stepwise multiple regression analyses, anxiety on the Hospital Anxiety and Depression scale and the dyspnea score tended to correlate more significantly with the single HRQoL values in both asthma and COPD than physiological measurements such as the forced expiratory volume in one second. The Hyland scale was less correlated with existing parameters (cumulative coefficient determination [R2] = 0.04) than the total HRQoL (cumulative R2 = 0.47) and the QWB scale (cumulative R2 = 0.49) in asthma. The single HRQoL values from the Hyland scale, the total HRQoL and the QWB scale evaluated different aspects of asthma and COPD. The psychological status and dyspnea contributed more significantly to the single HRQoL values in these two disorders than the physiological measurements. In asthma, the Hyland scale was especially different from the other single HRQoL scales and should be evaluated separately from the multi-item HRQoL assessments.