Quality-of-life assessment in respiratory disease: an examination of the content and validity of four questionnaires.

Four recent questionnaires for measuring the quality of life of patients with respiratory disease (Chronic Respiratory Disease Questionnaire, St George's Respiratory Questionnaire, Living with Asthma Questionnaire, and Asthma Quality of Life Questionnaire) differ in the content and style of the items used. Differences in content arise over the use or emphasis on symptom items, functional limitation (activity) items, and emotion items. These differences stem in part from the different methods used for item selection and refinement, which include selecting the most 'important' items, qualitative analysis for clarity, ratings of distress, and psychometric analysis. Despite these differences, there is considerable evidence for content validity of all four questionnaires. Because quality of life is so poorly developed as a theoretical construct, the demonstrable statement that all 4 questionnaires have construct validity provides little information about the questionnaires.