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It is pointed out that the familiar analytical device of "event tree", widely used in risk analysis, can be viewed as a transition matrix expressing the likelihood of going from "entry states" to "exit states". This point of view is shown to have numerous interesting conceptual and computational features which promise to make it a very useful addition to the arsenal of tools for risk analysis. The basic idea is explained first in terms of a simple, made‐up example. The application of the idea to a very real and complicated problem, nuclear‐plant risk assessment, is then outlined.

If the point of view is adopted that in calculations of real‐world phenomena we almost invariably have significant uncertainty in the numerical values of our parameters, then, in these calculations, numerical quantities should be replaced by probability distributions and mathematical operations between these quantities should be replaced by analogous operations between probability distributions. Also, practical calculations one way or another always require discretization or truncation. Combining these two thoughts leads to a numerical approach to probabilistic calculations having great simplicity, power, and elegance. The philosophy and technique of this approach is described, some pitfalls are pointed out, and an application to seismic risk assessment is outlined.

This article will not attempt to document the thesis that there are corporate abuses or that an enabling act is less desirable than a regulatory type of statute. It is sufficient to assert or presume that there may be internal corporate abuses and that it may be desirable for some states, if they so choose, to have corporation statutes which are more than enabling acts and which limit or regulate specified aspects of corporate conduct. The question of whether it is feasible for a state to maintain a corporation statute which attempts closely to regulate the internal affairs of the corporation is then posed. The answer to such an inquiry is necessarily intertwined with the practices by which corporate charters are issued by the various states and with the federal character of our governmental structure.

Die Autoren diskutieren zunächst verschiedene qualitative Aspekte des Risikobegriffs und gehen dann zu einer ersten quantitativen Definition über. Da der Begriff der "Wahrscheinlichkeit" mit der Risikodefinition zusammenhängt, ist ein weiterer Abschnitt der Klärung dieses Begriffs gewidmet. Dabei geht es um die sorgfältige Unterscheidung von "Wahrscheinlichkeit" und "Häufigkeit". Mit dieser Unterscheidung wird ein Risikobegriff entwickelt, der umfassend und flexibel genug ist, um sämtliche Aspekte und Feinheiten von Risiken zu erfassen, die während der Risikoabschätzung vorkommen können. (pmb)

A quantitative definition of risk is suggested in terms of the idea of a "set of triplets". The definition is extended to include uncertainty and completeness, and the use of Bayes' theorem is described in this connection. The definition is used to discuss the notions of "relative risk", "relativity of risk", and "acceptability of risk".

The North American Free Trade Agreement (NAFTA) and the General Agreement on Tariffs and Trade (GATT) have focused attention on risk assessment of potential insect, weed, and animal pests and diseases of livestock. These risks have traditionally been addressed through quarantine protocols ranging from limits on the geographical areas from which a product may originate, postharvest disinfestation procedures like fumigation, and inspections at points of export and import, to outright bans. To ensure that plant and animal protection measures are not used as nontariff trade barriers, GATT and NAFTA require pest risk analysis (PRA) to support quarantine decisions. The increased emphasis on PRA has spurred multiple efforts at the national and international level to design frameworks for the conduct of these analyses. As approaches to pest risk analysis proliferate, and the importance of the analyses grows, concerns have arisen about the scientific and technical conduct of pest risk analysis. In January of 1997, the Harvard Center for Risk Analysis (HCRA) held an invitation‐only workshop in Washington, D.C. to bring experts in risk analysis and pest characterization together to develop general principles for pest risk analysis. Workshop participants examined current frameworks for PRA, discussed strengths and weaknesses of the approaches, and formulated principles, based on years of experience with risk analysis in other setting and knowledge of the issues specific to analysis of pests. The principles developed highlight the both the similarities of pest risk analysis to other forms of risk analysis, and its unique attributes.