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uncertainties seems to require such a presentation of risk results. Although presenting a number of plausible risk estimates has the advantage that it would seem to more faithfully reflect the true state of scientific understanding, there are no well-established criteria for using such complex results in risk management.

The various approaches to dealing with uncertainties inherent in risk assessment are summarized in Table L-1.

As can be seen in the nutrient chapters, specific default assumptions for assessing nutrient risks have not been recommended. Rather, the approach calls for case-by-case judgments, with the recommendation that the basis for the choices made be explicitly stated. Some general guidelines for making these choices are, however, offered.

TABLE L-1 Approaches for Dealing with Uncertainties in a Risk Assessment Program

Program Model

Advantages

Disadvantages

Case-by-case judgments by experts

Flexibility; high potential to maximize use of most relevant scientific information bearing on specific issues

Potential for inconsistent treatment of different issues; difficulty in achieving consensus; need to agree on defaults

Written guidelines specifying defaults for data and model uncertainties (with allowance for departures in specific cases)

Consistent treatment of different issues; maximization of transparency of process; resolution of scientific disagreements possible by resort to defaults

Possible difficulty in justifying departure or achieving consensus among scientists that departures are justified in specific cases; danger that uncertainties will be overlooked

Presentation of full array of estimates from all scientifically plausible models by assessors

Maximization of use of scientific information; reasonably reliable portrayal of true state of scientific understanding

Highly complex characterization of risk, with no easy way to discriminate among estimates; size of required effort may not be commensurate with utility of the outcome



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