Air Pollution and Mortality in the Medicare Population

To the Editor: Di et al. (June 29 issue) 1 provide a sophisticated examination of the association between exposure to ozone concentrations and mortality among the Medicare cohort population. They frame the warm season in the years 2000 through 2012 to encompass the months of April through September. However, April through September is too long a period to be described as solely a warm season. The authors combine average ozone levels in three different seasons: spring (April through May), summer (June through August), and fall (September). In general, ozone concentrations over the United States are usually higher in the summer than . . .