A study of 1,600 counties across the United States, by physicist Bernard Cohen of the University of Pittsburgh and published in the journal Health Physics, found that counties with higher levels of residential radon gas had lower cancer rates. The study controlled for 54 other variables that might affect cancer rates, such as smoking and socioeconomic status. (Wealthier people can afford energy-efficient houses that readily trap the radon gas that seeps up from the ground.)

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