The added value of the EQ-5D with a cognition dimension in injury patients with and without traumatic brain injury

Purpose This study investigated the psychometric gain, if any, from the extension of the EQ-5D with a cognition bolt-on (EQ-5D + C) in a large cohort injury patients with and without traumatic brain injury (TBI). Methods Hospitalized adult injury patients filled out a survey 1 month after initial admission. The survey included the EQ-5D-3L, the cognition bolt-on item in EQ-5D format, and the visual analogue scale (EQ-VAS). We compared ceiling and other distributional effects between EQ-5D and EQ-5D + C and TBI and non-TBI group, and assessed convergent validity using the predictive association with EQ-VAS. Also, we assessed explanatory power using regression analysis, and classification efficiency using Shannon indices. Results In total, 715 TBI patients and 1978 non-TBI patients filled out the EQ-5D + C and EQ-VAS. Perfect health was reported by 7.9% (N = 214) on the EQ-5D, and 7.3% (N = 197) on the EQ-5D + C. Convergent validity was highest for EQ-5D + C in the TBI group (Spearman’s rank correlation coefficient = − 0.736) and lowest for EQ-5D in the non-TBI group (Spearman’s rank correlation coefficient = − 0.652). For both TBI and non-TBI groups, the explanatory power of EQ-5D + C was slightly higher than of EQ-5D (R2 = 0.56 vs. 0.53 for TBI; R2 = 0.47 vs. 0.45 for non-TBI). Absolute classification efficiency was higher for EQ-5D + C than for EQ-5D in both TBI groups, whereas relative classification efficiency was similar. Conclusions Psychometric performance in general of both the EQ-5D and EQ-5D + C was better in TBI patients. Adding a cognitive bolt-on slightly improved the psychometric performance of the EQ-5D-3L.