The key rule for evaluating options that include outcomes that are uncertain is the expectation principle: the value of being exposed to the possibility of an outcome is determined by the value of the outcome and the frequency with which it would be experienced if you were exposed to the possibility repeatedly. For example, facing an one-in-twelve chance of losing a year of life expectancy should be evaluated as facing a certain loss of one month (1/12th of a year) of life expectancy. The expected value of such an option is loss of a month of life.

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