Six Cities Revisited

To the Editor: The Six Cities Study by Dockery et al. 1 has captured renewed attention (Jan. 8 issue). 2 , 3 Claiming to identify an increased mortality rate in Steubenville, Ohio, as compared with the rate in Portage, Wisconsin, the authors posited that air pollution in Steubenville, an Ohio River Valley mining and steel-making city, was responsible for its increased death rate. That interpretation is not permissible, inasmuch as the socioeconomic and ethnic makeups of the populations of Portage and Steubenville are markedly different. Compounding that invidious comparison, the calculated difference in mortality rates is seen to be only a hair's breadth . . .