Quality of life in asthma: I. Internal consistency and validity of the SF-36 questionnaire

Asthma is a chronic disease in which social life is altered. The importance of restrictions on social life may be greater in severe asthma or when symptoms are not adequately controlled. General scales of quality-of-life (QOL) may be used to detect the importance of social life impairment, but it is not yet known whether the scores of such QOL measures are reliable and valid in asthmatic patients. A study was carried out in 252 patients with asthma of variable severity (FEV1 ranging from 25 to 131% of predicted) to assess the validity of a general QOL scale, the first French version of the SF-36 health status questionnaire (SF-36). This is based on 36 items selected to represent nine health concepts (physical, social, and role functioning; mental health; health perceptions; energy or fatigue; pain; and general health). All nine SF-36 category scores were highly significantly correlated with the severity of asthma assessed by the clinical score of Aas (p < 0.0007 to p < 0.0001). Eight SF-36 category scores were highly significantly correlated with FEV1 (p < 0.003 to p < 0.0001). A high internal reliability of SF-36 was found using the α coefficient of Cronbach (0.91 for the whole questionnaire). The SF-36 questionnaire is valid and reliable in asthma and can therefore be used to examine QOL in asthmatic and nonasthmatic patients and to determine to what extent asthma impairs social life.