Valuation of cognition bolt-ons for EQ-5D-5L in Japan: A comparative analysis of scaling factor and conventional models

BackgroundA cognition bolt-on version for EQ-5D is needed to comprehensively assess health states of the general population.ObjectiveTo experimentally evaluate the valuation methods of the EQ-5D-5L bolt-ons using scaling factor and conventional models, we used the cognition bolt-on version of the Japanese EQ-5D-5L (EQ-5D-5L + C) and two previously developed cognition dimensions Remembering things and Thinking clearly.MethodsEligible participants, recruited from the general Japanese population, included adults living in three cities. Interviews were conducted from June to August 2023. Participants were randomized to Arms 1 (EQ-5D-5L + C), 2 (EQ-5D-5L + Remembering things), and 3 (EQ-5D-5L + Thinking clearly). Preferences were collected using a composite time trade-off (cTTO). The "1-cTTO" data were modeled using the scaling factor model, with EQ-5D-5L disutility weights estimated from the existing value sets. We also fitted the data into the conventional main-effects additive model. Both models used a tobit model and maximum likelihood estimation. Model performance was assessed using indices of fit.ResultsOverall, 864 individuals participated in the study. Addition of cognition dimensions to EQ-5D-5L expanded the scaling factor model coefficients in all arms. The observed mean and predicted "1-cTTO" values of the scaling factor model were not largely different in all three arms. The mean absolute errors of the scaling factor and conventional models were 0.0720 and 0.1305, 0.0748 and 0.0885, and 0.0985 and 0.0685 in Arms 1, 2, and 3, respectively.ConclusionsThe performance of the two models did not appear greatly different. Further experimental valuation studies using the scaling factor model and cognition items are warranted.