Until the 1980’s, radon science relied solely on research of data from underground miners to predict the risk for people exposed to residential radon. However, several residential studies advanced research on the health effect of radon to more accurately assess risk to the general population. The types of residential studies were ecologic and case-control in nature. Ecologic studies tried to relate the number of lung cancer deaths for a region with substitute measures of exposure for that region. Many of these studies showed a relationship between exposure to radon and an increased risk of lung cancer. However, ecologic studies do not consider information on individual smoking history or mobility, both of which are important variables in assessing radon risk. Due to their high variability, ecologic studies were discontinued and replaced with the more reliable case-control study.
Case-control studies compared individuals with lung cancer (cases) to individuals without lung cancer (controls). Both groups were compared for differences in home exposures, again using substitute measures of radon exposure. A number of these studies found an association between indoor exposure to radon and increased lung cancer risk. Scientists determined that when taken individually, some studies don’t have the statistical power for conclusive reporting. For this reason, scientists decided to pool data from international studies as they are completed.
The North American Residential Radon Pooling Study, which includes the Iowa Lung Cancer Study [IRLCS] (Epidemiology, March 2005) and the European Residential Radon Pooling Study (British Medical Journal January 2005) combined data from twenty previous residential studies to confirm the radon risks predicted by extensive occupational studies of underground miners who breathed radon for a period of years. By pooling the residential data, studies showed an increased lung cancer risk consistent with the predicted 12% per 2.7 pCi/L based on a linear model developed by the National Research Council.
Further validating these studies, The World Health Organization (WHO) published the WHO Handbook on Indoor Radon, A Public Health Perspective, 2009. The Handbook definitively ends the need for extrapolation of data from miner studies and validates pooled residential studies as a direct method of estimating risks to people in the home. Furthermore, the WHO handbook concludes that exposures to low and moderate radon concentrations account for the vast majority of radon-induced lung cancers. According to EPA, these findings effectively end any doubts about the risks to Americans of having radon in their homes and confirm that breathing low levels of radon can lead to lung cancer. EPA also estimates over 21,000 deaths per year are caused by radon-induced lung cancer in the United States. The World Health Organization (WHO) estimates that radon causes up to 15% of lung cancers worldwide.