Association Between Ozone and Mortality Not Confounded by Temperature
Large multi-center studies in the U.S. and Europe have recently reported that ozone is associated with daily deaths, especially in the summer. Since ozone air pollution peaks in the summer months, it is difficult to control for the effects of high temperature.
This study employed a “case-crossover” technique to compare each subject’s characteristics and exposures at the time a death occurred, with a control period for the same subjects when the adverse event did not occur. This approach makes it possible to control for the effect of temperature on the day of death. Multiple cities must be included to provide sufficient statistical power for the analysis.
Cities studied were Birmingham AL, Boulder CO, Canton OH, Chicago IL, Cincinnati OH, Colorado Springs CO, Columbus OH, Detroit MI, Houston TX, New Haven CT, Pittsburgh PA, Provo UT, Seattle WA, and Spokane WA.
Close to 850,000 adult deaths were analyzed, along with data on ozone concentrations and temperature, for a 13 year period.
The author concludes that “the association between ozone and mortality risk is unlikely to be due to confounding by temperature.”
Schwartz J. How sensitive is the association between ozone and daily deaths to control for temperature? Am J Resp Crit Care Med 2004; doi 10.1164/rccm.200407-933OC, Online Dec. 3, 2004.
The American Thoracic Society offers the abstract online.
