Decision analysis is based on the normative expected utility theory (EUT; see Chapters 2 and 5; Elwyn et al 2001, Tavakoli et al 2000, Thornton 1996). Decision analysis is used prescriptively as a way of assisting decision makers with their choices. Underpinning the process is the assumption that humans are rational, logical decision makers. A rational decision, in the con- text of decision analysis, is one that results in the outcome with the greatest usefulness to the individual (Elwyn et al 2001).