by Howard Fienberg
The media are often accused of playing chicken little, shouting that the sky is falling, but a new study purports to show that chicken little was right. USA Today broke the story on February 28, with the front-page headline: Fallout likely caused 15,000 deaths. That night, it was covered by CNN, PBS Newshour, and most local TV news stations. The next day, other media followed with similarly scary headlines (Almost all in U.S. have been exposed, study finds, The New York Times; Nuke test fallout caused 15,000 deaths, Reuters; Most Americans were exposed to fallout, Deseret News). The study, from the Centers for Disease Control and Prevention (CDC) estimated that at least 15,000 cancer deaths in Americans born since 1951 were likely to have been caused by breathing or ingesting radioactive fallout from nuclear weapons testing.
According to the CDC study, it was limited to rudimentary evaluations of the average impact on limited health outcomes for the U.S. population. Unfortunately, while words like limited, estimate and uncertainty were littered throughout the study, they rarely surfaced in the media coverage.
The London Guardian claimed the study measured radioactive isotopes across the U.S. On the contrary, all the CDC researchers did was model the possible dispersal patterns of radioactive material from testing sites. From this model, they estimated the average dose of radiation each person received based on the presumed collective national dose.
In calculating the average dose, the researchers took account of domestic testing and above-ground tests conducted outside of the U.S. The researchers cautioned that the global doses have a larger degree of uncertainty. But considering that the estimate of domestic testings impact on thyroid cancer cases in the U.S. population varied between 11,300 and 212,000, the addition of estimated fallout from foreign tests to the equation would drive the margin of error into the stratosphere. In fact, the study noted that because the uncertainty in the preliminary doses estimated for this feasibility study has not been quantified, uncertainty in the risk of all cancers and leukemia cannot be fully evaluated.
As a result, the researchers stressed that the estimates of cancers linked to radioactive fallout were abstract and could in no way be attributed to individuals. The true risk to individuals in the United States may vary substantially from the average for many reasons, e.g. a difference in their dose from the predicted value, their lifestyle patterns, other environmental exposures, their individual susceptibility to radiation effects, and the random nature of the predicted risk. ... accurately determining the risk for specific individuals is not possible.
Separating radioactive fallout from the many other sources of background radiation would be difficult, and measuring its specific impact would be even more so. Nonetheless, headlines were sensational, and notes of caution only appeared deep inside the stories. Most media were at least careful to note that the fallout may have led to increased risk for certain cancers, not that it simply caused cancers. Some, like The New York Times, even noted that the average American had received almost 20 times as much radiation from medical procedures like chest X-rays as from fallout of all kinds over the same period. Others, like the Salt Lake Tribune, identified curious inconsistencies in the studys data. The Tribune quoted the director of the Utah Cancer Registry, who expressed surprise at the estimated cancer figures for Weber and Salt Lake counties, which have the lowest overall cancer deaths among the 50 state and the District of Columbia.
Steve Tetreault and Keith Rogers of the Las Vegas Review-Journal deserve special kudos for consulting a National Nuclear Safety Administration health physicist. His comments emphasized the significant margin of error in deriving expected deaths from the scant data available and said that the study, which revealed no new knowledge, was really a guess about the effects of small doses from radioactivity factored into a large number of people.
Unfortunately, even presuming the models and estimates of the amount of fallout were correct, the presumptions behind the estimated effects of the radiation may not be. The CDC study relied upon the linear no-threshold hypothesis (LNTH). LNTH presumes that with each incremental rise in radiation exposure, the health effects will rise a proportionate amount in a linear direction. It also assumes that any exposure to radiation is deleterious to human health, even the smallest amount that can be measured (hence the no-threshold). But many scientists question the veracity of the theory. Much evidence now points to some possible positive health effects of low-level radiation. In April 1999, the American Nuclear Society concluded that there is insufficient scientific evidence to support the LNTH in the projection of the health effects of low-level radiation. So, it seems, the study was based on unsteady theories as well as shaky estimates.
Because of all the uncertainties, theres no way to know how many people were exposed to how much radiation or what effects it might have caused. It is a pity that the media's knee-jerk reaction was to stir apocalyptic panic.
Howard Fienberg is senior research analyst with the non-profit non-partisan think-tank the Statistical Assessment Service (STATS), in Washington, DC.
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