The validity of a visual analogue scale in determining social utility weights for health states.

Asking people to place health states on a visual analogue scale is a commonly used technique for establishing social utility weights for life years. Recently, the technique has been adopted for setting priorities in the Oregon Medicaid Program in the US; as well as by the Euroqol Group in their development of an instrument meant to serve as a tool for linking cross-national valuations of health states. However, it is unclear what people mean when they value health states on a visual analogue scale. In a series of empirical studies, subjects expressed little depth of intention in relation to the valuations beyond the act of ranking states. Comparisons of the valuations, with valuations elicited by means of the equivalence of numbers technique, indicated that intervals between states on the visual analogue scale must be weighted more the closer they are to the bottom of the scale. This is the same as saying that visual analogue scale values should not be used directly as utility weights for life years. A transformation of the values is needed, and a power function may be suitable for this purpose.