IJE Advance Access originally published online on March 2, 2006
International Journal of Epidemiology 2006 35(3):779-786; doi:10.1093/ije/dyl022
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Association between reported exposure to road traffic and respiratory symptoms in children: evidence of bias
1 Swiss Paediatric Respiratory Research Group, Department of Social and Preventive Medicine, University of Berne, Switzerland
2 The Leicester Children's Asthma Centre, Division of Child Health, Department of Infection, Immunity & Inflammation, University of Leicester, Leicester, LE2 7LX, UK
* Corresponding author. Department of Social and Preventive Medicine, Finkenhubelweg 11, CH-3012 Bern, Switzerland. E-mail: kuehni{at}ispm.unibe.ch
Background Many studies showing effects of traffic-related air pollution on health rely on self-reported exposure, which may be inaccurate. We estimated the association between self-reported exposure to road traffic and respiratory symptoms in preschool children, and investigated whether the effect could have been caused by reporting bias.
Methods In a random sample of 8700 preschool children in Leicestershire, UK, exposure to road traffic and respiratory symptoms were assessed by a postal questionnaire (response rate 80%). The association between traffic exposure and respiratory outcomes was assessed using unconditional logistic regression and conditional regression models (matching by postcode).
Results Prevalence odds ratios (95% confidence intervals) for self-reported road traffic exposure, comparing the categories ‘moderate’ and ‘dense’, respectively, with ‘little or no’ were for current wheezing: 1.26 (1.13–1.42) and 1.30 (1.09–1.55); chronic rhinitis: 1.18 (1.05–1.31) and 1.31 (1.11–1.56); night cough: 1.17 (1.04–1.32) and 1.36 (1.14–1.62); and bronchodilator use: 1.20 (1.04–1.38) and 1.18 (0.95–1.46). Matched analysis only comparing symptomatic and asymptomatic children living at the same postcode (thus exposed to similar road traffic) showed similar ORs, suggesting that parents of children with respiratory symptoms reported more road traffic than parents of asymptomatic children.
Conclusions Our study suggests that reporting bias could explain some or even all the association between reported exposure to road traffic and disease. Over-reporting of exposure by only 10% of parents of symptomatic children would be sufficient to produce the effect sizes shown in this study. Future research should be based only on objective measurements of traffic exposure.
Keywords Child, preschool, asthma, cough, vehicle emissions, bias, epidemiological methods, questionnaires
Accepted 30 January 2006
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