The most elaborate case-control epidemiologic radon study performed by R. William Field and colleagues identified a 50% increased lung cancer risk with prolonged radon exposure at the EPA's action level of 4 pCi/L.[1] Iowa has the highest average radon concentrations in the United States and a very stable population which added to the strength of the study. For that study, the odds ratio was found to be increased slightly above the confidence interval (95% CI) for cumulative radon exposures above 17 WLM (6.2 pC/L=230 Bq/m3 and above).