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OP VII – 2 Does temperature confounding control influence the modifying effect of air temperature in ozone-mortality associations?
  1. Kai Chen1,
  2. Kathrin Wolf1,
  3. Regina Hampel1,
  4. Massimo Stafoggia2,
  5. Susanne Breitner1,
  6. Josef Cyrys1,
  7. Evangelia Samoli3,
  8. Zorana Jovanovic Andersen4,
  9. Getahun Bero Bedada5,
  10. Tom Bellander5,6,
  11. Bénédicte Jacquemin7,8,
  12. Juha Pekkanen9,10,
  13. Annette Peters1,
  14. Alexandra Schneider1
  1. 1Helmholtz Zentrum München, Institute of Epidemiology II, Neuherberg, Germany
  2. 2Lazio Region Health Service, Department of Epidemiology, Rome, Italy
  3. 3National and Kapodistrian University of Athens, cDepartment of Hygiene, Epidemiology and Medical Statistics, Athens, Greece
  4. 4University of Copenhagen, Department of Public Health, Centre for Epidemiology and Screening, Copenhagen, Denmark
  5. 5Karolinska Institutet, Intitute of Environmental Medicine, Stockholm, Sweden
  6. 6Stockholm County Council, Centre for Occupational and Environmental Medicine, Stockholm, Sweden
  7. 7INSERM-Ageing and Chronic Diseases, Epidemiological and Public Health Approaches (VIMA), Villejuif, France
  8. 8Barcelona Institute for Global Health – Campus MAR (ISGlobal),, Barcelona, Spain
  9. 9University of Helsinki, Department of Public Health, Helsinki, Finland
  10. 10National Institute for Health and Welfare (THL), epartment of Health Protection, Living Environment and Health Unit, Kuopio, Finland


Background/aim Recent epidemiological studies investigating the modifying effect of air temperature in ozone-mortality associations lack consensus as how to adjust for nonlinear temperature effect in addition to including an interaction term.

Methods We evaluated the influence of temperature confounding control on temperature-stratified ozone-mortality risks in a time-series setting in eight European cities and 86 U.S. cities, respectively. To investigate potential residual confounding, we additionally incorporated next day’s ozone in models with differing temperature control.

Results Using only a categorical variable for temperature or only controlling nonlinear effect of low temperatures yielded highly significant ozone effects at high temperatures, but also significant residual confounding in both regions. Adjustment for a nonlinear effect of temperature, especially high temperatures, substantially reduced ozone effects at high temperatures and residual confounding. For example, when using a distributed lag nonliner temperature term, risk estimates at low, medium, and high temperatures were 0.23% (95% CI: −0.09% to 0.55%), 0.23% (95% CI: −0.06% to 0.53%), and 0.36% (95% CI: 0.04% to 0.68%) in European cities, and 0.11% (95% CI: −0.31% to 0.54%), 0.17% (95% CI: −0.07% to 0.41%), and 0.59% (95% CI: 0.32% to 0.85%) in U.S. cities.

Conclusion Inadequate control for confounding by air temperature leads to residual confounding and an overestimation of the temperature modifying effect in studies of ozone-related mortality.

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