Figure 1. Model Schematic.

People with HD can enter the model in either the PFD, SF1, or SF2 health states, depending on the modeled population. As indicated by the straight arrows, they may then transition to more progressed health states at a constant rate of progression based on a simple linear regression of TRACK-HD^16,17 data. Alternatively, the curves arrows indicate they may remain in their previous health state. They may also transition to death at any time by US background mortality.¹⁵ In hypothetical comparisons with future disease-modifying treatments, the constant rate of transitions to more progressed health states is both arrested for a given amount of time and progression is slowed by a given rate ratio. PFD = prefunctional decline; SF2 = Shoulson and Fahn stage 2 (TFC 10-7); SF1 = Shoulson and Fahn stage 1 (TFC 13-11).