design paper

Populace dynamics: an open, scored longitudinal layer for policy microsimulation

The paper specifies Populace's longitudinal Dynamics layer — trajectory-weighted calibration, transitions as conditional models, domains of validity, and a scoring protocol under which every claim resolves, backtests, or computes exactly from statute. First validation domain: U.S. Social Security.

foundation

Builds on Populace's certified cross-sectional layer — 0.038 holdout loss vs 0.317 for the enhanced CPS it replaced.

method

One weight per trajectory with entry/exit markers; a Dynamics operator mixing deterministic hazards with machine-learned earnings processes.

discipline

No 75-year point forecasts — sensitivity surfaces instead; forecast cells resolve annually; contributions merge only on held-out score.

scope

U.S. Social Security is the first validation domain; the layer is country-agnostic by construction.