certain substances (food additives, pesticides, pharmaceuticals) develop the information needed to evaluate health threats, and they are further required to gain regulatory approvals to market their products. Products requiring premarket approval can be barred from commerce if regulators determine that their safety is questionable. In most cases, however, the agencies are required to develop health-related information, or to use information published in the scientific literature, to assess threats to health and to establish whether the threat is sufficient to support actions to reduce it. This latter model closely approximates the situation at DHS.

Until the mid- to late 1970s, agency approaches to what later came to be called risk analysis were not highly explicit, and they involved no clearly identified and scientifically justified methodology (NRC, 1983). Indeed, scientific and policy controversies of several kinds rose to the surface in the late 1970s and gave rise to much public concern over the use of scientific information by federal agencies. These concerns prompted a congressionally mandated review by the National Academies, resulting in a report entitled Risk Assessment in the Federal Government: Managing the Process issued by the National Research Council in 1983. That report, which is commonly known as “the Red Book,” contained a review and analysis of the scientific and policy controversies that had given rise to it (including allegations that federal risk assessments were often “manipulated” to yield the results desired by decision makers), and it offered a way forward that laid a foundation for risk analysis that continues to this day. Many critics of the 1983 report have focused on the awkwardness of the way it portrayed the relationships of analysis to decision making, and this problem has been corrected in the recent Science and Decisions report (NRC, 2008b). However, the principles for risk analysis set forth in the 1983 report remain in place, and they have been relied upon by the EPA and other federal agencies. The structure of the risk analysis process and definitions of key terms first handed down in the 1983 report remain in place.

Among the several key principles elaborated in the 1983 report, and affirmed in every expert report that has followed, is the need for care in making inferences beyond what has been shown rigorously. Risk-related information collected through various types of scientific investigations (observational and experimental studies) can reveal risks that directly apply only under limited conditions, and the use of such information to assess risks under different conditions requires the imposition of inferences from (or extrapolation beyond) the data. Two examples help to illustrate this problem:

  1. Studies in certain occupational settings in which workers were exposed to high levels of benzene have consistently provided an association between those exposures and excess risks of leukemia. The EPA and other agencies seek to understand whether benzene exposures experienced by the general population, exposures that are typically several orders of magnitude lower than those observed in the workplace, might also pose a risk of leukemia. OSHA is similarly concerned to understand whether the current occupational exposures, again



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