ICECAP-O, the current state of play: A systematic review of studies reporting the psychometric properties and use of the instrument over the decade since its publication.

Purpose: A paper reporting the development of the ICECAP-O was published in 2006. Since then, there has been increasing interest in the use of capability-based measures within health economics and the ICECAP-O has been suggested for use in economic evaluation by decision-making bodies in the Netherlands and UK. Methods: A systematic review of studies published between January 2006 and October 2018 which have assessed the psychometric properties of ICECAP-O or utilised the measure within economic evaluation. Results: Twenty-four studies explored the psychometric properties of ICECAP-O and 21 have utilised the measure within economic evaluation; one study reported psychometric properties as well as utilising the measure within economic evaluation. The ICECAP-O has good construct validity and responsiveness, but there is evidence of some issues relating to content validity. In the context of economic evaluation, the ICECAP-O has, to date, mainly been included as a secondary economic measure and the reporting of results is brief with minimal detail and often no discussion. Five of the economic evaluation studies combined scores from ICECAP-O with time, but each used different terminology to describe this result. Conclusion: Focus, in terms of publications, appears to have shifted now from assessment of psychometric properties to the utilisation of the ICECAP-O within economic evaluation. Further research is needed with respect to a decision-rule for the ICECAP measures. This additional research should also guide users in terms of appropriate analysis, terminology and presentation of results, which are in-keeping with the conceptual framework underpinning the ICECAP-O.