The certain and sure money or utility ('sure thing') that a subject would have to receive to be indifferent between it and a given gamble ('uncertain prospect') is called the gamble's 'certainty equivalent'. The certainty equivalent is less than the expected value of the gamble if an individual has a diminishing marginal utility of money income and obeys the axioms of expected utility theory. This indicates a kind of risk aversion. In health economics, the usual experiment contains a certain outcome, such as five years of healthy life, and an uncertain prospect consisting of the combination of two or more uncertain outcomes such as probability p of having two years of healthy life and probability (1 - p) of having 15 years of healthy life. P is then experimentally adjusted until there is indifference.
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