Re: The Diesel Exhaust in Miners Study: A Nested Case–Control Study of Lung Cancer and Diesel Exhaust and a Cohort Mortality Study With Emphasis on Lung Cancer When the Diesel Exhaust in Miners Study

(DEMS) was initiated in the early 1990s, one key goal was to develop quantitative estimates of historical exposure to diesel exhaust (DE). It was recognized that the epidemiological results would only be as robust as the exposure assessment upon which they are based. Respirable elemen-tal carbon (REC), a surrogate of diesel exhaust particulates, was selected as the primary exposure variable, yet in very recent years investigators turned to an alternative exposure assessment method-ology that relied instead on carbon mon-oxide (CO) measurements. Assumptions were also made regarding engine horse