Design of exposure questionnaires for epidemiological studies.

Correspondence to: Dr M J Nieuwenhuijsen, Imperial College of Science, Technology and Medicine, London, UK; m.nieuwenhuijsen@imperial. ac.uk _________________________ Q uestionnaires are frequently used in the exposure assessment of occupational and environmental epidemiological studies. Questionnaires may be the method of choice for assessing exposure because no other sources of information are available, or because they provide the most efficient data collection method, allowing a larger study size and greater statistical power than would be possible with other more accurate measurement techniques. They may be used in combination with other methods. Information on presence of exposure (yes/no), duration, frequency, and pattern of exposure is often obtained by questionnaire. Very few, if any, standardised questionnaires that have been validated are available in this area. This is one of the major limitations of questionnaires and researchers should be extremely careful how they use self-reported exposure since it may bias the exposure-disease association. The design of new questionnaires often depends on the experience acquired with previous questionnaires. Questionnaires require careful consideration of design and administration issues, including, for example, the length, detail of the required information, logistics, participation and completion rate, and costs involved. 2 Exposures of interest may often be past exposures; subjects may not be able to recall these which may lead to underreporting. Furthermore, lack of understanding of the questions or knowledge of the exposure may bias the reporting. Recall bias, where those with disease are more likely to report their exposures compared to those without disease, even though there is no true difference, needs to be avoided; this requires careful consideration of the questions that are asked.