Potential sources of bias in the use of individual's recall of the frequency of exposure to air pollution for use in exposure assessment in epidemiological studies: a cross-sectional survey

BACKGROUND: In a previous study it has been shown that mean population perception of air pollution correlates well with physical measures of actual air pollution and could be used as a measure of exposure to air pollution, at least for those forms of pollution perceptible to humans. However, for such a measure to be valid researchers would need to be confident that it was not strongly biased by possible confounding variables. This study reports the association between perception of above average levels of air pollution compared with others in the neighbourhood and a number of factors that may influence reporting. METHODS: This was a postal cross-sectional study of 3402 households in England in a mixed rural and urban area adjacent to a large industrial complex. Respondents were asked about their social and demographic characteristics, the presence of respiratory symptoms and frequency of exposure to a range of pollution types. RESULTS AND DISCUSSION: There were strong associations (p < 0.01) with the presence of a person in the home with respiratory symptoms, the belief that industrial pollution was harming their health, social class, living in rented accommodation and reporting noise from neighbours and other people's smoke. Smoking behaviour did not affect reporting. CONCLUSIONS: We did not find any evidence of bias that would substantially invalidate mean population reporting of air pollution severity as a measure of exposure in epidemiological studies, though care may be needed in interpreting results where those factors found to be significant in this study vary substantially between areas.