IDEAS home Printed from
   My bibliography  Save this paper

Assessing the Health Effects of Air Pollution Using the Case-Crossover Design


  • Holly Janes

    (University of Washington)

  • Lianne Sheppard

    (University of Washington)

  • Thomas Lumley

    (University of Washington)


The case-crossover design has been widely used to study the association between short term air pollution exposure and the risk of an acute adverse health event. The design uses cases only, and compares exposure at the event time with exposure at other control or "referent" times. By making within-person comparisons, time invariant confounders are controlled. Time varying confounders can also be controlled by design if referents are matched on these factors. Yet, proper referent selection is important for other reasons. The design involves an implicit assumption that the distribution of exposure is constant across referent times. In addition, the statistical method usually used to analyze a case-crossover study, conditional logistic regression, is only unbiased with certain referent strategies. This paper reviews the case-crossover literature in the air pollution context, and clarifies key referent selection issues. It concludes with a set of recommendations for choosing a referent strategy with air pollution exposure data. The time stratified approach to referent selection is advocated, as it ensures unbiased conditional logistic regression estimates and avoids bias due to time trend in the exposure series. The particular stratification can be tailored to control for time varying confounders by design.

Suggested Citation

  • Holly Janes & Lianne Sheppard & Thomas Lumley, 2004. "Assessing the Health Effects of Air Pollution Using the Case-Crossover Design," UW Biostatistics Working Paper Series 1046, Berkeley Electronic Press.
  • Handle: RePEc:bep:uwabio:1046

    Download full text from publisher

    File URL:
    Download Restriction: no

    More about this item


    case-crossover design; air pollution;


    Access and download statistics


    All material on this site has been provided by the respective publishers and authors. You can help correct errors and omissions. When requesting a correction, please mention this item's handle: RePEc:bep:uwabio:1046. See general information about how to correct material in RePEc.

    For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: (Christopher F. Baum). General contact details of provider: .

    If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

    We have no references for this item. You can help adding them by using this form .

    If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your RePEc Author Service profile, as there may be some citations waiting for confirmation.

    Please note that corrections may take a couple of weeks to filter through the various RePEc services.

    IDEAS is a RePEc service hosted by the Research Division of the Federal Reserve Bank of St. Louis . RePEc uses bibliographic data supplied by the respective publishers.