Geo Testing

Turns spend up or down in selected regions and compares outcomes against matched control regions to estimate causal effect.

You pair similar markets on historical sales, change spend in the test set, and model what the test regions would have done without the change. Because it works on aggregate regional revenue, it survives cookie loss entirely and can measure channels no pixel reaches. It suits national advertisers with enough geographic spread. The pitfall is contamination, whether media spillover across market boundaries or a promotion that ran in one region.