Asthma is a common and potentially serious disease. Its frequency and severity seem to be increasing in several countries. It is very important that good epidemiological data are available so that changes over time and geographical differences in prevalence can be monitored. Numerous surveys have been conducted in different countries, and there is a large body of literature on the subject. It is, however, very difficult to compare the results of surveys conducted at different times or in different places because of the absence of a standard definition of asthma which is suitable for epidemiological studies. Most surveys of asthma employ questionnaires. These offer several advantages over other methods of ascertaining asthma in large numbers of subjects (e.g. inhalation and exercise challenge tests). They are widely acceptable, cheap, and convenient, requiring no special equipment. They are reasonably independent of the immediate circumstances, such as time of year, atmospheric temperature, upper respiratory tract infection, and current treatment, which may affect the results of provocation tests. They are also easy to standardize, at least when selfadministered. It therefore seems somewhat surprising that as yet no questionnaire is widely accepted for this purpose. The simplest type of question that can be used to ascertain asthma relates to the subject's own opinion: 'Have you ever had asthma?' This is remarkably specific (at any rate within Britain), in that people who claim to have the disease nearly always seem in fact to have it [1]. It is, however, seriously insensitive: a substantial number of both children [2] and adults [1,3] are unaware of having asthma but would be so diagnosed if clinically investigated. There is little added advantage in asking whether asthma has ever been diagnosed by a doctor, since the answer is dependent on the subject's readiness to consult doctors, the number of doctors consulted, and the subject's memory of what the doctors said. Furthermore, the diagnosis of asthma is susceptible to changes in doctors' readiness to attach the label of 'asthma' to patients with minor respiratory symptoms, and there is a widespread impression that asthma is now being diagnosed more readily than it used to be, both among children and in older adults. There is therefore a good case for asking subjects about their symptoms rather than about the diagnosis that has been attached to those symptoms. The cardinal symptoms of asthma are wheeze and breathlessness, so questions about these symptoms form part of asthma questionnaires. It cannot be assumed, however, that these questions are entirely unambiguous. Members of nonwheezy families do not necessarily know what a wheeze is, and may use the term for a variety of noises and sensations. When questionnaires are used for international comparisons, there may be no exact equivalent of wheeze in different languages. And even if these difficulties can be surmounted, there is no set of answers which have been shown to correspond exactly with the clinical diagnosis of asthma. The International Union Against Tuberculosis and Lung Disease (IUATLD) has produced a questionnaire designed for use in epidemiological studies of asthma. This questionnaire was formulated in English and translated into French, German and Finnish, and was found to give reproducible results in all four languages [1]. Its sensitivity and specificity have been assessed using the bronchial response to histamine as the 'gold standard'; this criterion may be questioned (as the investigators themselves point out [4]), since bronchial reactivity is not specific to asthma and is strongly related to cigarette smoking. On this basis, wheeze was a particularly sensitive symptom, but no one symptom was especially specific in all four centres. Reported asthma was highly specific, especially in Britain, and it is noteworthy that this was still the case when a doctor's opinion (rather than bronchial hyperreactivity) was used to define the diagnosis. An attempt has now been made to improve the diagnostic efficiency of the questionnaire method by presenting questions in a video recording. There are obvious advantages in this approach, and the paper by the New Zealand group [5] compares it with the IUATLD questionnaire. The responses to the video questionnaire were significantly more reproducible than those to the written questionnaire, while the specificity and sensitivity were at least as good, in terms of bronchial reactivity to methacholine. The subjects were schoolchildren aged 1316 years of high socio-economic status, who cannot be assumed to respond in the same way as the general population. The authors consider that the written questionnaire would be more easily answered by their subjeets than by schoolchildren generally, so that the advantages of the video questionnaire should be even greater in the general population than in this group. The method is certainly an attractive one, and may well mark a real improvement in questionnaire methods. It is
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