Startup Runway
Live · model v1.2sim_runwayOwner Tom Reyes · EconomicsUsed in Why Prices Rise (card 9) and the rent caps trendSample data
Preview draft
Fix 2 failing scenarios first
Editing draft v2.4 · Saved 10:18
Brief and goal
- XP on completion
- 40 XP · sim.complete
- Level
- Level 3 · Reader and up
- Typical time
- 6 min
- Model version
- v2.4 draft · from v2.3
Fixed disclaimer · shown on every simulation, cannot be editedThis is a simplified model for learning. Real cities differ, and economists disagree about how large these effects are.
Controls 5 parameters
| Label | Key | Min | Max | Step | Default | Unit |
|---|---|---|---|---|---|---|
| Rent cap | rent_cap_pct | 50 | 120 | 5 | 90 | % of market rent |
| Years since the cap | years | 0 | 10 | 1 | 3 | years |
| How fast landlords respondDefault 0.5 → 0.4 | supply_elasticity | 0.1 | 2.0 | 0.1 | 0.4 | elasticity |
| How much renters want to move | demand_elasticity | 0.1 | 2.0 | 0.1 | 0.4 | elasticity |
| Exempt new buildings | exempt_new | — | — | — | Yes | on / off |
Outcome tiles
Preview at default settings, year 3 · draft v2.4
Flats for rent9,200−8.0% vs no cap
Waiting list640households
Average rent paid90index, market = 100
Upkeep94index, year 0 = 100
Assumptions shown to learners
- 1. The city starts at 10,000 flats at market rent.
- 2. No new public housing is built.
- 3. Landlords can sell to owner-occupiers.
Real-world case[CITY] rent regulation, [YEAR]: what studies found about supply and rents, with 2 sources both ways.Case needs a fact-check pass
Test harness
Run today 10:21 by Tom Reyes · draft v2.4 against live v2.3 · 48 scenarios46 passed2 failed
| Scenario | Inputs | Expected | v2.3 live | v2.4 draft | Result |
|---|---|---|---|---|---|
| A cap above market rent changes nothing | rent_cap_pct=120 | 10,000 | 10,000 | 9,640 | Fail |
| Waiting list is never negative | supply=0.1 demand=2.0 | ≥ 0 | 0 | −120 | Fail |
| A cap at market rent equals no cap | rent_cap_pct=100 | 10,000 | 10,000 | 10,000 | Pass |
| A tighter cap never adds flats | rent_cap_pct 90→80 | falls | 8,800→7,900 | 9,200→8,400 | Pass |
| Exempting new buildings helps supply by year 5 | exempt_new on/off, years=5 | on > off | 8,950 > 8,600 | 9,050 > 8,700 | Pass |
| Same inputs give the same outputs | 1,000 repeat runs | spread < 1% | 0.2% | 0.3% | Pass |
Showing 6 of 48 · failures first