Derivation of a UK preference-based value set for the Short Warwick-Edinburgh Mental Well-being Scale (SWEMWBS) to allow estimation of Mental Well-being Adjusted Life Years (MWALYs)

Background: The Mental Well-being Adjusted Life Year (MWALY) is an alternative outcome measure to the quality-adjusted life year (QALY) in economic evaluations of interventions aimed at improving mental well-being. However, there is a lack of preference-based mental well-being instruments for capturing population mental well-being preferences. Objectives: To derive a UK preference-based value set for the Short Warwick-Edinburgh Mental Well-being Scale (SWEMWBS). Methods: 225 participants that were interviewed between December 2020 and August 2021 completed 10 composite time trade-off (C-TTO) and 10 discrete choice experiment (DCE) interviewer-administered exercises. Heteroskedastic Tobit and conditional logit models were used to model C-TTO and DCE responses respectively. The DCE utility values were rescaled to a C-TTO comparable scale through anchoring and mapping. An inverse variance weighting hybrid model (IVWHM) was used to derive weighted-average coefficients from the modelled C-TTO and DCE coefficients. Model performance was assessed using statistical diagnostics. Results: The valuation responses confirmed the feasibility and face validity of the C-TTO and DCE techniques. Apart from the main effects models, statistically significant associations were estimated between the predicted C-TTO value and participants' SWEMWBS scores, gender, ethnicities, education levels, and the interaction terms between age and useful feeling. The IVWHM was the most optimal model with the fewest logically inconsistent coefficients and the lowest pooled standard errors. The utility values generated by the rescaled DCE models and the IVWHM were generally higher than those of the C-TTO model. The predictive ability of the two DCE rescaling methods was similar according to the mean absolute deviation and root mean square deviation statistics. Conclusions: This study has produced the first preference-based value set for a measure of mental well-being. The IVWHM provided a desirable blend of both C-TTO and DCE models. The value set derived by this hybrid approach can be used for cost-utility analyses of mental well-being interventions.