Setting: Whereas prevalence studies usually involve a general population sample, morbidity studies often involve the evaluation of factors that affect asthma severity within an asthmatic population.
Objective: To review methods of measuring morbidity in adult asthmatics, and to assess the appropriateness of the available methods in a variety of research contexts.
Findings: As in prevalence studies, symptoms are the cornerstone of studies of asthma morbidity. These may be supplemented by physiological measures including daily peak flow measurement, but bronchial hyper-responsiveness (BHR) testing is usually impractical, and there is no simple relationship between current asthma severity and current levels of BHR in individuals. Health service and medication usage are often taken as measures of asthma morbidity, but they may be inappropriate in studies in which increased contact with the health services is an intended or unintended effect of participation. Measures of quality of life can be a useful complement to more 'objective' methods.
Conclusions: In studies of morbidity in adult asthmatics, the emphasis should be on using 'appropriate methodology', and methods that may be appropriate in one context may be completely inappropriate in another.