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Issues in Risk Assessment (1993)


« Previous: Implications of Uncertainty for Ecological Risk Assessment
Suggested Citation:"VALUATION." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.

The group noted that the degree of uncertainty that is acceptable in a study depends on the costs associated with the outcome of the risk assessment, the magnitude of expected effects, and the availability of alternatives to the hazardous agent being addressed. In the TBT study, although there were many uncertainties, once the risk to oysters was established, uncertainties about effects on other organisms were unimportant. The availability of alternatives to TBT as an antifouling agent further reduced the importance of the uncertainties.

Recommendations for Dealing With Uncertainty
  • A discussion of uncertainty should be included in any ecological risk assessment. Uncertainties could be discussed in the methods section of a report, and the consequences of uncertainties described in the discussion section. End point selection is an important component of ecological risk assessment. Uncertainties about the selection of end points need to be addressed.

  • Where possible, sensitivity analysis, Monte Carlo parameter uncertainty analysis, or another approach to quantifying uncertainty should be used. Reducible uncertainties (related to ignorance and sample size) and irreducible (stochastic) uncertainties should be clearly distinguished. Quantitative risk estimates, if presented, should be expressed in terms of distributions rather than as point estimates (especially worst-case scenarios). Power analysis or a discussion of sample size should be included in all studies involving collection of data and testing of hypotheses.

  • A continuing program of monitoring and experimental testing is needed to improve the accuracy and credibility of the process of ecological risk assessment. There are few standards for judging the accuracy of assessments, and continuing checks need to be made to increase confidence in the process.


W. Desvousges and R. Johnson

The discussion leaders began by summarizing their view of the role

Suggested Citation:"VALUATION." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.

of valuation in ecological risk assessment. Managing ecological risks requires a consistent means of comparing alternatives. Monetary values are an appropriate basis for such comparisons. Economic concerns influence several components of the risk assessment process, including hazard identification (which end points are worthy of societal concern?) and risk characterization (what are the economic implications of uncertainty?). Cost-benefit analyses are frequently a key aspect of risk management decisions.

The discussion leaders presented some methods for valuing ecological resources based on two assumptions of classical welfare economics—that societal values are sums of individual values and that people know and can express their willingness to pay (or accept compensation) for various risk policies. They then discussed some aspects of risk that influence individual decisions about willingness to pay or accept compensation:

  • Amount, content, frame, and source of information;

  • Decision heuristics;

  • Cause of damage;

  • Responsibility;

  • Degree of suffering;

  • Immediacy or delay of effects;

  • Morbidity or mortality.

They then discussed specific issues related to determining willingness to pay for preserving ecological resources. For recreational-use values (such as fishing, hunting, and birdwatching), techniques for valuation are reasonably well established. Current research in valuation focuses on nonrecreational values. There are two principal types of such values: ecological services (sometimes called services of nature) and existence value. Ecological services are services provided by ecosystems that otherwise would have to be provided by technology. The role of wetlands in pollution abatement and flood control is a good example of an ecological service. Existence values, more vaguely defined and more controversial, are defined by people's willingness to pay for the existence of particular populations or ecosystems, even if they never expect to use or see them.

The discussion leaders presented a tutorial on methods used to elicit existence values with questionnaires. There was much heated discussion.

Suggested Citation:"VALUATION." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
Page 329
Suggested Citation:"VALUATION." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
Page 330
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The scientific basis, inference assumptions, regulatory uses, and research needs in risk assessment are considered in this two-part volume.

The first part, Use of Maximum Tolerated Dose in Animal Bioassays for Carcinogenicity, focuses on whether the maximum tolerated dose should continue to be used in carcinogenesis bioassays. The committee considers several options for modifying current bioassay procedures.

The second part, Two-Stage Models of Carcinogenesis, stems from efforts to identify improved means of cancer risk assessment that have resulted in the development of a mathematical dose-response model based on a paradigm for the biologic phenomena thought to be associated with carcinogenesis.

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