• Although a diagnosis of thyroid cancer must be treated seriously, it is an uncommon cancer and is rarely life threatening. Most individuals exposed to I-131 fallout from the Nevada weapons tests—even those few whose doses approached or exceeded 1 gray (Gy, 100 rad) are unlikely to develop exposure-related thyroid problems. Communicating small probabilities and changes in small probabilities may be difficult.

  • A widespread attempt to alert the public to the possible health consequences of exposure to I-131 fallout and to promote systematic screening for thyroid cancer might not lead to entirely benign outcomes. No evidence shows that screening for thyroid cancer is effective in improving survival for this highly survivable disease. Screening tests are imperfect and can cause harm in the form of unnecessary surgeries and other procedures, anxiety, insurability problems, and other problems. The quality of the tests also depends on the skill of the screeners, which can vary widely.

Despite the complexity of the topic, the uncertainty of estimates of exposure and of probabilities of developing cancer, and public questions about government credibility, DHHS must devise ways to communicate accurately, credibly, and effectively about its 1997 (NCI 1997a) report (taking into account sound criticisms of its methods, conclusions, and presentation). Media and other attention to the report and to the fallout issue more generally will undoubtedly attract interest and concern and lead some people to want to learn more about their own potential chance of developing health problems. The committee believes that DHHS must accept responsibility for helping people understand the possible relevance of the NCI report to their own circumstances but recognizes that the limits of available data and methods will make this difficult.

The following sections of this chapter discuss characteristics and principles of risk communication that emphasize how people construct their own judgments of risk; the importance of source credibility in those judgments; the probability that the audience for risk information will be heterogeneous rather than homogeneous, thus creating the need for a variety of different information efforts; and the need to promote involvement rather than exclusion of the public in the risk communication process. The chapter also explores some specific communication strategies aimed at both groups and individuals. The resources and effort expended on risk communication should be proportional to the potential for harm and the likelihood that the risk communication will be successful.

CHARACTERISTICS OF RISK COMMUNICATION

As is the case with most risks, communicating effectively possible health hazards stemming from exposure to I-131 fallout from the Nevada nuclear-weapons tests will be complicated. Most risk communication efforts fail because communicators believe the process is relatively simple: ''educate the public" (Liu



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