region rather than in unpopulated regions in Central America as a whole. In some northwestern Iowa and southwestern Minnesota counties, the outdoor radon concentrations exceed the national average indoor radon concentrations. Despite the above average, both Minnesota and Iowa's numbers were exceptionally close, regardless of the distance. Accurate doses of radon is heavily needed to further understand the problems radon in total can have on a community. It is understood that radon poisoning does lead to bad health, and lung cancer, but with further research, controls could change results in radon emissions both inside and outside of housing units. Radon exposure (mostly radon daughters) has been linked to lung cancer in numerous case-control studies performed in the US, Europe and China. There are approximately 21,000 deaths per year in the US due to radon-induced lung cancers. In Slovenia, a country with a high concentration of radon, about 120 people yearly die because of radon. One of the most comprehensive radon studies performed in the US by epidemiologist R. William Field and colleagues found a 50% increased lung cancer risk even at the protracted exposures at the EPA's action level of 4 pCi/L. North American and European pooled analyses further support these findings. However, the discussion about the opposite results is still continuing, especially a 2008 retrospective case-control study of lung cancer risk which showed substantial cancer rate reduction for radon concentrations between 50 and 123 Bq/m3. Most models of residential radon exposure are based on studies of miners, and direct estimates of the risks posed to homeowners would be more desirable. Because of the difficulties of measuring the risk of radon relative to smoking, models of their effect have often made use of them. Radon has been considered the second leading cause of lung cancer and leading environmental cause of cancer mortality by the EPA, with the first one being smoking. Others have reached similar conclusions for the United Kingdom and France. Radon exposure in homes and offices may arise from certain subsurface rock formations, and also from certain building materials (e.g., some granites). The greatest risk of radon exposure arises in buildings that are airtight, insufficiently ventilated, and have foundation leaks that allow air from the soil into basements and dwelling rooms. Thoron (220Rn) was measured at comparatively high concentrations in buildings with earthen architecture, such as traditional half-timbered houses and modern houses with clay wall finishes. Because of