Estimating an exchange rate between the EQ-5D-3L and ASCOT

Background The aim was to estimate an exchange ratebetween EQ-5D-3L and the Adult Social Care OutcomeTool (ASCOT) using preference-based mapping via com-mon time trade-off (TTO) valuations. EQ-5D and ASCOTare useful for examining cost-effectiveness within thehealth and social care sectors, respective ly, but there is apolicy need to understand overall benefits and compareacross sectors to assess relative value for money. Standardstatistical mapping is unsuitable since it relies on concep-tual overlap of the measures but EQ-5D and ASCOT havedifferent conceptualisations of quality of life.Methods We use a preference-based mapping approach toestimate the exchange rate using common TTO valuationsfor both measures. A sample of health states from eachmeasure was valued using TTO by 200 members of the UKadult general population. Regression analyses are used togenerate separate equations between EQ-5D-3L andASCOT values using their original value set and TTOvalues elicited here . These are solved as simultaneousequations to estimat e the relationship between EQ-5D- 3Land ASCOT.Results The relationship for moving from ASCOT to EQ-5D-3L is a linear transformation with an intercept of-0.0488 and gradient of 0.978. This enables QALY gainsgenerated by ASCOT and EQ-5D to be compared acrossdifferent interventions.Conclusions This paper estimated an exchange ratebetween ASCOT and EQ-5D-3L usin g a preference-basedmapping approach that does not compromise the descrip-tive systems of the two measures. This contributes to thedevelopment of preference-based mapping through the useof TTO as the common metric used to estimate theexchange rate between measures.