U

a state in which the true value of a parameter or the structure of a process is unknown

A measure of preference for a specific health outcome, obtained by methods that involve uncertainty (e.g., standard gamble approach).  Utilities are usually expressed on a cardinal scale of zero to one (e.g. death typically has a utility value of zero and a full healthy life has a value of one) and are used as health-related quality of life weights to calculate QALYs.