What the Cross-Retailer Halo Effect Reveals About Siloed Attribution
Most brands measure their retail media campaign at the retailer where the ad ran. That seems logical, but it’s also wrong in ways that are costing real money.
Incremental analyzed more than 150,000 campaigns representing $350M in ad spend and found a consistent pattern across all four retail media networks studied: a meaningful share of every campaign's impact lands somewhere other than the retailer that served the ad. We call this the cross-retailer halo effect, and siloed attribution misses almost all of it.
The measurement problem hiding in plain sight
Retail media has always relied on closed-loop attribution. A shopper sees an ad on Retailer A, buys at Retailer A, the campaign gets credit. Clean and clear. But shoppers don't behave that way.
Cross-shopping is the norm, not the exception. Consumers research on one platform and buy on another. They see an ad online and walk into a store. They buy from a competitor of the retailer that ran the ad. None of that shows up in the standard attribution report.
This was always a limitation. It became a serious one as commerce media moved up the funnel. Search campaigns, which capture high-intent shoppers close to purchase, largely stay within the retailer environment. DSP campaigns, which operate at awareness and consideration, do not. When you run a display or video campaign through a retail media network, you are generating demand that converts across the entire retail ecosystem, not just on the platform that measured it.
What the data shows
The cross-retailer halo effect is not a rounding error.
For off-site DSP campaigns, more than 50% of total measured impact occurred at retailers other than the one that ran the ad. Off-site video had the strongest cross-retailer signal, with 62% of impact occurring off-retailer. Even on-site DSP, running within a retailer's own environment, showed 29% of impact landing elsewhere.
The in-store dimension compounds this further. DSP campaigns drove 40%+ of their impact in physical stores, across both the primary retailer and others. Online ads are creating real foot traffic that last-touch attribution never captures.
When Incremental factored in the portion of each brand's retail universe not included in the study, the estimated share of retail media impact being missed by siloed measurement today is between 36% and 53%. For off-site video specifically, that figure reaches 67-80%.
There has been a systematic underreporting of ROI that leads directly to under-investment in upper-funnel retail media.
Why this matters now
Brand dollars are flowing into retail media networks at scale. Retail media ad spend is projected to reach $70B in the U.S. in 2026, with 70% of that spend incremental to existing trade budgets. The majority is funded by brand and media dollars, not shopper budgets.
But brand dollars carry brand objectives: building equity, driving growth across all sales channels, generating demand that pays off over time. Measuring those dollars against a single retailer's closed-loop report creates a structural mismatch between what the investment is supposed to do and how its performance is judged.
The result is a vicious cycle. Campaigns look underperforming, brand budgets shift toward lower-funnel tactics, upper-funnel air cover thins out, and lower-funnel efficiency declines. The fix is not to abandon retail media. It is to measure it correctly.
The path forward
Cross-retailer incrementality measurement changes what you can see. Rather than asking "did this campaign drive sales at this retailer," it asks "did this campaign drive incremental sales across the full universe of channels where my customers buy." That is the question that aligns with how brand dollars actually work.
Incremental's full analysis covers the methodology, the findings across search and DSP, and what a two-lens measurement framework looks like in practice.
