1. BACKGROUND The last twenty-five years have seen a large amount of psychological research in the area of behavioral decision theory. It followed the major breakthrough of decision theory that came with von Neumann and Morgenstern's Theory of Games and Economic Behavior in 1944. The key concepts are probability as a measure of uncertainty and utility as a measure of value and risk. The theory prescribes, given some behavioral axioms, that alternatives should be ranked in accordance with their expected utilities. Psychologists became interested in studying how people's decision behavior...