rDxt steps down in January 2024 #16

For every location except US, rDxt drops by about 3% between December 2023 and January 2024.

• adj_rDxt() holds rDxt at its 2010-2020 mean from 2022 (R/adj_rDxt.R; called at R/param_initial.R:623-625)
• the COVID return ramp ends December 2023 at the February 2020 value (R/process_simulations.R:52-57)
• California: 0.3187 in December 2023, 0.3098 in January 2024

Not introduced in this fork.

Fix on branch model-fixes.

Line numbers refer to branch rsims-wrapper at 209120a, as of 2026-11-03.