Empirical comparison between capability and two health-related quality of life measures

The Investigating Choice Experiments Capability Measure (ICECAP) is a new preference-based measure of the extent to which a person is able to achieve attributes or capabilities related to the quality of life. Conceptually, it differs from health-related quality of life (HRQoL) as the focus is upon the ability or capacity to achieve as distinct from the current experience of the attributes. The objective of this study was to explore the empirical relationships between capability as assessed by the ICECAP for Adults (ICECAP-A) and HRQoL as assessed by the Assessment of Quality of Life (AQoL)-8D and the five-level EuroQol Five Dimensions questionnaire (EQ-5D). To compare these measures, the study employed self-reported survey data from the healthy public and from seven disease areas in five countries. Results indicate that, despite their conceptual origins, the ICECAP-A is strongly associated with the AQoL-8D and that the clear distinction between capabilities and HRQoL found in other studies is attributable to the use of the EQ-5D in the comparison and the weaker association between the EQ-5D and ICECAP-A. The suggestion that ICECAP-A should be included in evaluation studies along with a HRQoL instrument is more persuasive when the instrument is the EQ-5D. The case for its inclusion with other HRQoL instruments requires further research and evaluation.