Model structure: VNS and RPS
vitiligo
REGRESSION, VITILIGO
For VNS and RPS, due to the discrete nature of the categories and initial plots (Supplementary Figure 
The parameters, α, β, γ and δ each refer to a general intercept, scale, shape, and asymptote (e.g., to ensure estimates to not exceed 1).Models M6 were fitted as follows:

Since VNS has 5 categories and RPS has 4, a polynomial regression of orders 4 and 3 were fitted to ensure adequate degrees of freedom to estimate all parameters. For RPS, a covariate for vitiligo location was included to compare utility predictions between hands/feet and head/face, this covariate was not statistically significant and not included in the final model however results for the inclusion of this covariate are reported in Supplementary Table 