SF-6D versus EQ-5D: reasons for differences in utility scores and impact on reported cost-utility

The choice of instrument (e.g. EQ-5D vs. SF-6D) can lead to different health-related utility scores, but it is unclear why these differences arise and whether they change cost utility analysis (CUA) results. This paper addresses these issues using a case study where using SF-6D rather EQ-5D led to greater utility gain and a lower cost per QALY for treatment. The paper examines reasons for this difference. This paper finds that an important factor was the inclusion in the SF-6D descriptive system of separate items for "vitality" and "social functioning", not explicitly included in EQ-5D. Further studies are required that examine the impact of the choice of instrument on cost-utility.