What if c 4 to 6 pCi/L were a "threshold"? If below that, down to c 1.0 pCi/L there was a lower risk of cancer than either more OR LESS radon concentration, both could be correct.
Do you have data to compare lung cancer rates where radon was 2-4 pCi/L with locations having <1.0 pCi/L? You wrote that most Iowa controls as well as cases had exposure to > 5.0 pCi/L radon, far above the USA average for Cohen-studied counties.
Howard Long
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