Beyond Uncertainty Factors: Protecting the Tails of the Bell Curve

Abstract

Back in 1988, Bernard Weiss, now professor emeritus at the University of Rochester Medical Center, calculated that if the mean IQ of a hypothetical population of 100 million people fell by 5 points, then the number scoring below 70—a threshold for requiring remedial assistance—would swell from 6 million to 9.4 million.1 Graphed on what’s known as a normal distribution in statistics, Weiss’ analysis revealed how a shift in the population mean—in this case for IQ but conceivably for other physical features such as weight, cholesterol levels, and attention span—can be particularly harmful to certain segments of society. Shifting means don’t occur spontaneously, however—they have a cause. A hypothetical drop in mean IQ, for instance, might result from widespread elevation in blood lead levels, and an increase in mean weight might result in part from widespread dietary changes or exposure to obesogens. And some individuals have predisposing risk factors that make them uniquely sensitive to the effects of these environmental stressors. For these vulnerable populations, a shift in the mean, as evidenced by Weiss’ calculation, could have disproportionate consequences. How to identify and then protect vulnerable subgroups has been a long-standing challenge for environmental risk assessment. Now risk assessors are starting to leverage new data coming from genomics, molecular epidemiology, and other fields in an effort to set targeted exposure limits that protect defined groups of people. The questions being asked are similar to discussions around personalized medicine, says Bill Farland, senior vice president for research at Colorado State University and former director of the National Center for Environmental Assessment in the U.S. Environmental Protection Agency (EPA) Office of Research and Development. “How far can we go towards protecting specific subgroups as opposed to relying on one-size-fits-all approaches?” he asks. “We need to bring more science into the discussion, and that’s what the field is confronting.”