In regulation of exposures to hazardous environmental agents, epidemiologic evidence is especially important in defining human risk estimates. The process of developing appropriate regulations is complex, however, and depends on many considerations beyond those established to a high degree of scientific certainty. Thus the needs of regulatory agencies are involved in the way epidemiologic data ...

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 sin...