Content validity, face validity and comprehensiveness of generic quality-of-life measures in adults and children with rare genetic conditions and their carers: a think aloud qualitative study

Purpose : This study aims to assess the content validity, face validity and comprehensiveness of the EQ-5D-5L, EQ-HWB, and ASCOT SCT4, for adults with rare genetic conditions; the EQ-5D-5L, EQ-HWB, and ASCOT-carer for carers of adults and children with rare genetic conditions; and the EQ-5D-Y-5L proxy-complete for carers of children with rare genetic conditions. Methods: 60 qualitative think-aloud interviews were conducted in Australia and England to understand the thought processes of participants as they completed QoL measures. After the completion of the measures, participants were led through a semi-structured discussion. Transcripts were analysed to understand whether participants could complete measures without the introduction of error. Thematic analysis was conducted on responses to the semi-structured discussion. Results: The overall error rate was very low (1-6%) and a greater proportion of participants reported that the instruments captured their quality-of-life than did not. Several non-health domains were identified as important, including treatment availability; impact on employment and finance; information and uncertainty; medication and carer burden; impact of passing on a condition; relationships and social connection; and experience with the healthcare system. Conclusion: The evidence suggests that the measures are comprehensive, and valid in measuring domains of importance. Future research should explore the extent to which the measures capture differences and changes in the QoL domains identified as important to patients and carers.