Nov 20, 2013

Mortality Displacement as a Function of Heat Event Strength in 7 US Cities

Saha, Michael V., Davis, Robert E., Hondula, David M.
American Journal of Epidemiology
  • States that mortality rates increase immediately after periods of high air temperature
  • States that in the days and weeks after heat events, time series may exhibit mortality displacement—periods of lower than expected mortality
  • Examines all-cause mortality and meteorological data from 1980 to 2009 in the cities of Atlanta, Georgia; Boston, Massachusetts; Minneapolis–St. Paul, Minnesota; Philadelphia, Pennsylvania; Phoenix, Arizona; Seattle, Washington; and St. Louis, Missouri
  • Models baseline mortality using a generalized additive model
  • Defines heat waves as periods of 3 or more consecutive days in which the apparent temperature exceeded a variable percentile
  • Calculates the sum of excess and deficit mortality for each heat wave 
  • Mortality displacement, which is the ratio of grand sum deficit to grand sum excess mortality, decreased as a function of event strength in all cities
  • Finds that displacement was close to 1.00 for the weakest events, and at the highest temperatures, displacement varied from 0.35 (95% confidence interval: 0.21, 0.55) to 0.75 (95% confidence interval: 0.54, 0.97)
  • Finds strong evidence of acclimatization across cities
  • States that without consideration of displacement effects, the net impacts of heat-wave mortality are likely to be significant overestimations