title: Comparison of different methods in analyzing short-term air pollution effects in a cohort study of susceptible individuals.
abstract: BACKGROUND
  Short-term fluctuations of ambient air pollution have been associated with exacerbation of cardiovascular disease. A multi-city study was designed to assess the probability of recurrent hospitalization in a cohort of incident myocardial infarction survivors in five European cities. The objective of this paper is to discuss the methods for analyzing short-term health effects in a cohort study based on a case-series.
  
  
  METHODS
  Three methods were considered for the analyses of the cohort data: Poisson regression approach, case-crossover analyses and extended Cox regression analyses. The major challenge of these analyses is to appropriately consider changes within the cohort over time due to changes in the underlying risk following a myocardial infarction, slow time trends in risk factors within the population, dynamic cohort size and seasonal variation.
  
  
  RESULTS
  Poisson regression analyses, case-crossover analyses and Extended Cox regression analyses gave similar results. Application of smoothing methods showed the capability to adequately model the complex time trends.
  
  
  CONCLUSIONS
  From a practical point of view, Poisson regression analyses are less time-consuming, and therefore might be used for confounder selection and most of the analyses. However, replication of the results with Cox models is desirable to assure that the results are independent of the analytical approach used. In addition, extended Cox regression analyses would allow a joint estimation of long-term and short-term health effects of time-varying exposures.
authors.affiliation: GSF-National Research Center for Environment and Health, Institute of Epidemiology, Neuherberg, Germany. peters@gsf.de
authors.forename: Annette
authors.initials: A
authors.lastname: Peters
authors.forename: Stephanie
authors.initials: S
authors.lastname: von Klot
authors.forename: Niklas
authors.initials: N
authors.lastname: Berglind
authors.forename: Allmut
authors.initials: A
authors.lastname: Hörmann
authors.forename: Hannelore
authors.initials: H
authors.lastname: Löwel
authors.forename: Fredrik
authors.initials: F
authors.lastname: Nyberg
authors.forename: Juha
authors.initials: J
authors.lastname: Pekkanen
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Perucci
authors.forename: Massimo
authors.initials: M
authors.lastname: Stafoggia
authors.forename: Jordi
authors.initials: J
authors.lastname: Sunyer
authors.forename: Pekka
authors.initials: P
authors.lastname: Tiittanen
authors.forename: Francesco
authors.initials: F
authors.lastname: Forastiere