[Contribution of case-crossover design to the analysis of short-term health effects of air pollution: reanalysis of air pollution and health data].
BACKGROUND
During the last decades, numerous studies have shown significant links between short-term exposure to air pollution and health. Time series design have been widely used in order to study these associations. In recent years, the case-crossover design has been applied to the analysis of acute effects of environmental exposures, especially air pollution. The aims of this paper are to describe the case-crossover design and to compare this approach with time series design to assess the association between air pollution and health.


METHODS
In the case-crossover approach, a case-control study is conducted whereby each person who had a health event (case period) is matched with himself/herself on a nearby time period where he/she did not have the event (control period). Review of the literature shows that the referent selection strategies can be associated to a bias in the estimation of the health effect of air pollution. In comparison with time series design, the case-crossover design is easier to conduct, and individual factors can be taken into account. Nevertheless, it is not possible to take into account the overdispersion in the health indicator with this approach.


CONCLUSIONS
In conclusion, we suggest to use time series analysis with population data and case-crossover design with individual data.
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ORS Ile-de-France, 21-23 rue Miollis, Paris cedex 15, France. ors-idf@ors-idf.org
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Pedrono
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Gremy
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D000397:Air Pollution / Q000032:analysis*; D016022:Case-Control Studies; D018592:Cross-Over Studies; D004781:Environmental Exposure; D004812:Epidemiologic Methods; D006801:Humans