Donor Quality

Donor quality has two distinct meanings in GeoSC.

The donor stage measures pairwise pre-period similarity. Correlation captures co-movement; RMSE and MAPE capture level error; normalised DTW captures temporal shape. Composite scores are relative within each treated geography and support screening. They do not estimate final counterfactual weights.

Inference measures joint synthetic-control fit. Several individually modest donors can combine well, while a highly correlated donor can receive little weight. Review fitted pre-period error and the SparseSC weight distribution.

Strong screening scores do not establish donor exchangeability. Eligibility also requires no treatment exposure, comparable outcome measurement, and no post-launch shock that differentially moves the donor. Conversely, poor overlap, incomplete metrics, concentrated recommendation weights, or weak joint pre-fit are direct reasons to reconsider the design.

Donor selection must be outcome-blind with respect to the measured post period. Changing the pool after seeing lift invalidates ordinary interpretation unless the search and multiplicity are explicitly modelled.