Comments

Biostatistics Advance Access published online on January 20, 2006. (Biostatistics, doi:10.1093/biostatistics/kxj017). http://biostatistics.oxfordjournals.org/cgi/content/abstract/kxj017v1

Abstract

Recently there has been increased interest in modelling the association between aggregate disease counts and environmental exposures measured, for example via air pollution monitors, at point locations. This paper has two aims: first we develop a model for such data in order to avoid ecological bias; second we illustrate that modelling the exposure surface and estimating exposures may lead to bias in estimation of health effects. Design issues are also briefly considered, in particular the loss of information in moving from individual to ecological data, and the at-risk populations to consider in relation to the pollution monitor locations. The approach is investigated initially through simulations, and is then applied to a study of the association between mortality in the over 65’s in the year 2000, and the previous year’s SO2, in London. We conclude that the use of the proposed model can provide valid inference, but the use of estimated exposures should be carried out with great caution.

Disciplines

Disease Modeling | Epidemiology