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Why should probabilistic risks analysis be performed?

For purposes of discussion, three reasons are proposed:

  1. Regardless of our ideological view of disasters and their causes, we would all agree that preferences can be established, so that for a given frequency of occurrence (e.g., a disaster occurring once every ten years), we prefer a disaster of small impact to one of major impact. Therefore, the scale of a disaster is relevant, and we have an obligation to establish ways to measure that scale.
  2. For a disaster of a specific scale, we would also prefer it to occur infrequently rather than frequently.  Therefore, a disaster’s frequency of occurrence is relevant and must be taken into account in any risk assessment.
  3. A high degree of uncertainty is present in virtually every risk assessment made. If we are to act rationally, this uncertainty cannot be ignored; instead, it must be acknowledged, processed, and incorporated in our assessments.

Probabilistic risk analysis is a technique that facilitates sensible resolution of the above-mentioned problems: the need for a measurement of the scale of a disaster, the relevance of its frequency of occurrence, and our obligation not to proceed as if no uncertainty were present.