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With reference to the paper by Aylin et al1 published in the March 2001 issue of Thorax, we would like to raise the following points.
Previous studies have concentrated on acute ill health due to particulate emissions but chronic effects have been neglected. This paper aimed to address this issue, with consideration being given to “at risk” groups. However, only acute events requiring hospital admission were included, with no consideration being given to those patients in the community with established cardiorespiratory disease. All studies have limitations but these should not be so significant as to invalidate the outcome. The authors recognised many of their limitations, such as socioeconomic factors and hospital variation, but others such as occupational exposure of the older population and emission differences between the sites and their surrounding industries were not considered. In addition, the authors failed to address major limitations from previous studies so the opportunities presented by such a large study were wasted because previous mistakes were repeated. Overall, these influences are so significant that any outcome cannot be considered valid, and hence no conclusions can be drawn.
We suggest that any follow up studies should take advantage of the effective population criteria used in this study and should include a more concise explanation of study design, time scale, statistical protocol, and emission data.