Mark Twain noted that there are "Lies, damned lies and statistics." In the world of asbestos and mesothelioma studies, there are lots of statistics. The risk posed by asbestos exposure is terrifically difficult to gauge, because there is no known safe exposure level to asbestos fibers, which means even a single exposure could lead to the development of an asbestos-related disease.
Another difficulty is determining the exact source of the risk. In Minnesota, the region known as the "Iron Range" has produced iron ore from taconite for more than a century. In a recent study, the occurrence of mesothelioma among miners has been found to be unusually high. The miners developed mesothelioma at a rate double what would be expected.