Purpose: To compare the measurement precision and related properties between the 5-level EuroQoL Group's 5-dimension (EQ-5D-5L) questionnaire and the Functional Assessment of Cancer Therapy-Breast (FACT-B) questionnaire in assessing breast cancer patients.
Methods: An observational study of 269 Singaporean breast cancer patients. To compare discriminative ability and responsiveness, the effect sizes (in standard deviation) of the EQ-5D-5L and the FACT-B in relation to health indicators and the change in performance status or quality of life were estimated. Test-retest reliability was examined using the intraclass correlation (ICC).
Results: Using performance status, evidence of disease, and treatment status as the criteria, the differences (FACT-B minus EQ-5D-5L) in the effect size for discriminative ability were negative or closed to zero, and the 90% confidence intervals totally fell within the zone that indicated the non-inferiority of the EQ-5D-5L. For responsiveness and test-retest reliability, the confidence intervals of the differences in effect size and ICC overlapped the non-inferiority margin; thus, non-inferiority in these two aspects could neither be confirmed nor rejected.
Conclusions: The EQ-5D-5L was non-inferior to the FACT-B in discriminating breast cancer patients with different health conditions cross-sectionally. The EQ-5D-5L serves as a reasonable alternative or supplementary instrument to the FACT-B in assessing breast cancer patients' health outcomes.