Signals

An anomaly signal = a district's z-score versus the other districts of the same city that period.

For each district we compute the z-score of its rent per m² and of its supply change against the distribution of all the city's districts that same period (population z-score). The signal takes the sign of whichever metric deviates most (|z|). The trigger is |z| ≥ 1.5σ.

Trigger threshold: |z| ≥ 1.5σ. Baseline: The baseline is the cross-section of Warsaw districts this period (peer comparison), not a single district's time series.