The results of a methodical ten-year-long, case-controlled study of residential radon exposure in Worcester County, Massachusetts, found an apparent 60% reduction in lung cancer risk amongst people exposed to low levels (0–150 Bq/m3) of radon gas; levels typically encountered in 90% of American homes—an apparent support for the idea of radiation hormesis.[78] In that study, a significant result (95% CI) was obtained for the 75-150 Bq/m3 category. The study paid close attention to the cohort's levels of smoking, occupational exposure to carcinogens and education attainment.