This work was conducted during the stay of J. Pekkanen in New Zealand with funding from the Academy of Finland and the Foundation for Allergy Research. The Wellington Asthma Research Group is supported by a Programme Grant from the Health Research Council of New Zealand, and by a major grant from the Guardian Trust (Trustee of the David and Cassie Anderson Medical Charitable Trust).
Defining asthma in epidemiological studies
Article first published online: 25 DEC 2001
European Respiratory Journal
Volume 14, Issue 4, pages 951–957, October 1999
How to Cite
Pekkanen, J. and Pearce, N. (1999), Defining asthma in epidemiological studies. European Respiratory Journal, 14: 951–957. doi: 10.1034/j.1399-3003.1999.14d37.x
- Issue published online: 25 DEC 2001
- Article first published online: 25 DEC 2001
- bronchial hyperreactivity;
- sensitivity and specificity;
It has been suggested that, in epidemiological studies, asthma should be defined as symptomatic bronchial hyperresponsiveness (BHR). This paper critically examines the validity of this and alternative methods of defining asthma by reviewing population-based studies validating BHR and symptom questionnaires against asthma defined on the basis of a clinical assessment. It is emphasized that a single definition of asthma will not be applicable to all studies.
When the aim of a study is to compare differences in prevalence of asthma between populations, Youden′s Index (sensitivity + specificity - 1) is the best single measure of validity. BHR has similar or better specificity, but much worse sensitivity, and therefore a worse Youden′s Index, than symptom questionnaires. When the aim is to estimate relative risks, the validity of the definition of asthma depends more on its positive predictive value. Therefore, more specific methods of detecting asthmatics, such as severe symptoms, diagnoses of asthma, or symptomatic BHR may be most useful in cohort and case-control studies. In contrast, conversely, the method of choice for the first phase of prevalence comparisons is standardized written or video symptom questionnaires.
In order to explore reasons for the differences in asthma prevalence, and to estimate possible differential symptom reporting, questionnaires can be supplemented with bronchial hyperresponsiveness and other testing in subsamples of the symptomatic and nonsymptomatic subjects. However, symptoms and bronchial hyperresponsiveness should usually be analysed separately rather than combined due to the poor agreement between bronchial hyperresponsiveness and clinical asthma.