Metrics
Halo / spillover effect
Lift in unattributed channels driven by paid spend on other channels.
Halo (or spillover) is the secondary lift in branded search, direct, and organic-social conversions caused by paid-spend awareness in another channel. Most often seen with TV, YouTube, and CTV — branded search rises 20–80% on weeks with heavy upper-funnel spend. Affiliate operators typically don't capture halo benefit; advertisers do, which is why some advertisers will pay an affiliate-rate premium even on under-attributed channels.
Example
DTC brand running CTV with $0.20 CPM spends $80K in March; branded-search Google volume rises 38% the same month, driving an extra $120K direct-response revenue not credited to the CTV buy.