QLU-C10D Validation: Assessing Ceiling Effects and Content Overlap with EQ-5D-5L

The measurement properties of QLU-C10D were effectively validated in this study. The lower ceiling effects of C10D's dimensions, which are related to the design of the questionnaire itself, can be attributed to its broader structural width compared to 5L. In this study, it was found that even among patients who were deemed completely healthy based on EQ-5D-5L, some still reported issues when using the cancer-specific measurements of C10D. Specifically, out of the 25 patients who selected '11111' on the 5L scale, 17 of them did not choose any option on the C10D scale (Table 3). Notably, C10D highlighted more concerns in the dimensions of Physical, Social, and Fatigue. Different from the study by Norma B. Bulamu et al., apart from Social and Fatigue, we also found some discrepancies in the results generated by the two scales in the Physical dimension when patients answered the questions. This is related to the greater inclusion of 5L content in the Physical dimension of C10D, such as mobility, self-care, and usual activities. Consequently, there is a significant overlap in the content of these two scales, supported by our convergent validity results that indicated higher correlations between theoretically corresponding domains and an overall strong association between the index scores.