THE CONSTRUCTS OF ASTHMA QUALITY-OF-LIFE - PSYCHOMETRIC, EXPERIMENTALAND CORRELATIONAL EVIDENCE

Health-related quality of life (QOL) questionnaires are designed to be content valid and cover several domains of life experience. We examin ed the QOL constructs of asthma by factor analysing responses of 810 a sthmatics to the Living with Asthma Questionnaire. Oblique rotation sh owed two cognitive factors (activities and avoidance) and two emotiona l factors (distress and preoccupation), and these factors were highly correlated due to a general factor of disease severity. The factors, i .e., the asthma constructs, did not coincide with the content valid do mains of the questionnaire. In a second study on a further 118 mild to moderate asthmatics whose asthma was poorly controlled, the physiolog y of asthma was manipulated experimentally with the new asthma medicin e, salmeterol, and quality of life and lung function measured. Lung fu nction and change in lung function correlated more highly with cogniti ve than emotional constructs. Under double blind conditions salmeterol compared with salbutamol improved quality of life significantly on th e constructs of activities, avoidance and preoccupation but not distre ss; there were improvements on all constructs after a period of open l abel treatment. The differential responsiveness to change of the QOL c onstructs may be due to their different relationships with lung functi on, and these data provide evidence for a multi-construct approach to QOL change.