Define Treatment and Donor Eligibility

Create and freeze an eligibility table before running GeoSC. Treat it as the analysis-universe contract: it records which geographies are treated, which untreated geographies are eligible controls, which geographies are excluded, and why.

Use one row per geography:

Column	Purpose
`unit_id`	Geography identifier used in the input panel.
`role`	`treated`, `eligible_control`, or `excluded`.
`included_in_panel`	Whether the unit is present in the versioned panel used by a stage.
`reason`	Design reason for inclusion or exclusion.
`decision_date`	Date the eligibility decision was made.
`owner`	Person or team accountable for the decision.
`contamination_notes`	Known campaign, operational, or measurement contamination.
`leakage_notes`	Geographic adjacency or audience leakage concerns.

Example:

unit_id	role	included_in_panel	reason	decision_date	owner	contamination_notes	leakage_notes
`region_ne`	`excluded`	`false`	Adjacent to treatment region and exposed to overlapping out-of-home media.	`2026-08-05`	Measurement lead	Same creative ran during the test window.	Commuter leakage into treatment area.

Eligible controls should be unaffected by treatment, measured consistently, and plausible counterfactual contributors. Pre-period correlation and donor-screen scores are diagnostics; they are not eligibility rules and do not prove exchangeability. Exclude geographies only for design reasons established before reviewing post-treatment outcomes.

Freeze the Universe

Define treated units and the first observed treatment period.
Remove contaminated, leaking, inconsistently measured, or otherwise ineligible controls.
Materialise the approved treated units and eligible controls as a versioned panel.
Run power, donor evaluation, and inference from that versioned panel.
If donor screening changes the eligible universe, create a new panel version and rerun the affected stages.

Do not tune exclusions, treatment dates, or donor membership after seeing post-treatment lift. That creates a different design and invalidates ordinary interpretation unless the search and multiplicity are explicitly modelled.

What GeoSC Includes

Power treats every non-treatment unit in its input as a control. Donor evaluation scores every eligible non-treatment unit in its own input. Inference uses the controls in its prepared panel, where controls are units without a treatment period. GeoSC does not automatically apply donor recommendations to the other stages.

For several treated geographies, confirm that the eligible control pool can support joint in-space placebo assignments: with $N_0$ controls and $N_1$ treated units, the exhaustive assignment count is $\binom{N_0}{N_1}$ , provided $N_0 \geq N_1$ . If the eligible control pool is too small, placebo inference is infeasible or too coarse for the planned alpha.

See also Donor Quality and the end-to-end synthetic study.