[Short-term relationships between urban atmospheric pollution and respiratory mortality: time series studies]

Time series studies conducted in the field of air pollution aim at testing and quantifying short-term relations which can exist between daily air pollution levels and daily health effects. The method used for this type of survey has sometimes been misunderstood mainly because individual factors and indoor exposure to air pollutants were not taken into account. The adjustment on these individual confounding factors commonly used in classic epidemiologic studies (case-control studies, cohort studies) is not adequate to times series studies which are based on aggregate data. This is different for those factors that change over time according to the levels of air pollution (meteorological conditions, influenza epidemics, trend of health cases) which, when being analysed, must be taken into account either indirectly through time modelling or directly through non-linear modelling processes. During this last decade, numerous studies using the time series method have been published and have found short-term associations between daily levels of air pollution commonly observed and daily respiratory mortality. The consistency of the numerous results published in the international literature are more arguments in favour of non-confounding short-term relations between air pollution and respiratory mortality.