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Risks induced by extreme events are characterized by small or ambiguous probabilities, catastrophic losses, or windfall gains. Through a new functional, that mimics the restricted Bayes‐Hurwicz criterion within the Choquet expected utility approach, it is possible to represent the decisionmaker behavior facing both risky (large and reliable probability) and extreme (small or ambiguous probability) events. A new formalization of the precautionary principle (PP) is shown and a new functional, which encompasses both extreme outcomes and expectation of all the possible results for every act, is claimed.

If information is too vague and imprecise to be summarized by a unique additive probability measure, an agent faces Knightian uncertainty or ambiguity rather than risk. Under Knightian uncertainty, an agent's beliefs may be represented by a capacity or a set of additive probabilities. It is proved that an agent's attitude towards ambiguity has a crucial role in asset price determination and portfolio choice. Knightian uncertainty attitude provides an alternative explanation of financial market failures and enables puzzles to be solved, such as market breakdowns, price indeterminacy and volatility, bid and ask spreads, portfolio inertia, violation of call and put parity.(J.E.L.: D81, G11, G12).

The notion of intertemporal h-option value is introduced to extend to environmental decision-making problems of the concept of quasi-option value, defined by Arrow and Fisher and Henry, whenever an individual faces imprecise information, or hard uncertainty, represented by a non-additive measure over events. Under hard uncertainty and irreversibility, the decision-maker faces the intertemporal h-option value, that is an uncertainty premium of preservation, which represents the gain from being able to learn about the future consequences of irreversible actions. The intertemporal h-option value is a correction factor that has to be taken into account in evaluating the total economic value of feasible actions.

The precautionary principle (PP) has been proposed as the proper guide for the decision‐making criteria to be adopted in the face of the new catastrophic risks that have arisen in the last decades. This article puts forward a workable definition of the PP based on the so‐called α‐maximin expected utility approach, applying it to the possible outbreak of the avian flu disease among humans. Moreover, it shows how the shortage and/or lack of effective drugs against the infection of the virus A(H5N1) among humans can be considered a precautionary failure.

In recent years the understanding of the cognitive foundations of economic behavior has become increasingly important. This volume contains contributions from such leading scholars as Adam Brandenburger, Michael Bacharach and Patrick Suppes. It will be of great interest to academics and researchers involved in the field of economics and psychology as well as those interested in political economy more generally