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Risk Evaluation and the Probability-Threshold Position

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Risk Analysis and Scientific Method

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Abstract

In a recent article in American Scientist, a scientist and public policy expert quipped: “Chicken Little is alive and well in America”.1 Never in history have health and environment-related hazards been so low, he said, while “so much effort is put into removing the last few percent of pollution or the last little bit of risk”.2 His thesis, like that of many others, was that our criteria for defining ‘acceptable risk’ often are too stringent.

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References

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  61. This probability is generally accepted in the U.S. nuclear industry. It is given in: U.S. Nuclear Regulatory Commission, Reactor Safety Study — An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants, Report No. (NUREG-75/014) WASH-1400, Government Printing Office, Washington, D.C., 1975, pp. 157 ff; hereafter cited as: WASH-1400. Note, however, that when this probability is applied to all nuclear plants now under construction or in operation, the lifetime probability of a core melt is 1 in 4. (For these calculations, see K. Shrader-Frechette, Nuclear Power and Public Policy, second edition, Reidel, Boston 1983, pp. 84–85; hereafter cited as: Nuclear Power.

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  70. This is exactly the case with the risk of nuclear core melt. See note 61 earlier.

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  72. A similar example of the context-dependent character of nuclear probabilities is given in Shrader-Frechette, Nuclear Power, pp. 84–85. Here the author shows how the same core melt probability, 1 in 17,000 reactor years can also be translated as 1 in 4, given 150 reactors operating for 30 years. See note 61.

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  77. In an earlier work, Okrent and several other assessors proposed a much more defensible version of the threshold hypothesis. They argued that technological risks could be classified as essential, beneficial, or peripheral to society, and that the maximum acceptable risk to the individual was different, depending on the risk classification. Risks in the first class were acceptable if they posed no higher than a 10–4 annual probability of death. Those in the second class, if they posed no greater than a 10–5 probability, and those in the third class, if they posed no more than a 10–6 probability. The chief merit of this earlier formulation is that it appears to take some account of the reasons why a particular threshold might be acceptable. If does not appear to rest on the implausible assumption of the later article, viz., that probability (or magnitude) alone is a sufficient condition for determining whether a risk is negligible. (See Okrent and Whipple ASRAC, pp. 8, 19, 20.)

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  78. Zracket, Remarks, p. 3.

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  79. See endnotes 7 and 8 above.

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  80. Shrader-Frechette, Science Policy, Chapters 8–9, discusses this point.

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  1. Dept. of Philosophy, University of Florida, USA

    K. S. Shrader-Frechette

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© 1985 D. Reidel Publishing Company

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Shrader-Frechette, K.S. (1985). Risk Evaluation and the Probability-Threshold Position. In: Risk Analysis and Scientific Method. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-5241-6_5

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  • DOI: https://doi.org/10.1007/978-94-009-5241-6_5

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