ABSTRACT
Further methodological problems arise in epidemiological studies. Questionnaires are the most widely used method to assess asthma status in population samples. At present, there are two main standardized respiratory symptom questionnaires available for children, one developed by the American Thoracic Society (1), the other by the International Study of Asthma and Allergies in Childhood (ISAAC) (2). When considering a parent's report of asthma as evidence of disease prevalence, one must bear in mind that parental responses are affected by patterns of use of medical care and by the choice of diagnostic labels by individual physicians. Estimates based on parental reports of wheeze may be affected by language barriers. In some languages, for example, there is no term for wheeze. Surveys that refer solely to a physician's diagnosis of asthma may pick out subjects with more severe illness and may therefore skew the reported characteristics of the condition. Conversely, studies that use the presence of wheezing as an indicator of asthma may overestimate the prevalence of the disease because of the poor specificity of wheezing symptoms for asthma.
