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Halo effect

The halo effect is the rise in sales or searches in one channel caused by advertising in another, such as Meta or YouTube ads lifting Google Shopping sales.

How it works

A shopper watches a Meta video ad without clicking, and a week later searches Google for the product and buys through a Shopping ad. Google Ads credits the Shopping click; the Meta ad is not in its path. So one channel’s effect lands in another channel’s report: more branded search, more Shopping or Performance Max sales, more marketplace orders (reporting when half your sales are on marketplaces).

An attribution model can’t prove a halo, because each platform shares credit only among the interactions it recorded. Proof needs an experiment: switch the other channel on or off in some regions or periods and compare Google sales there with the rest (checking the cross-channel halo effect). A study of one high-end clothing retailer found that its advertising lifted sales in the other sales channel (online or stores) almost as strongly as in its own, measured as elasticities.

Example

Example store, not client data.

The tableware shop adds Meta ads at 10,000 a month, and Meta credits itself with 30,000 of sales: a ROAS of 3.0. Google Ads spend stays at 40,000, but its revenue rises from 180,000 to 198,000.

If a test shows the extra 18,000 appears only where Meta ran, Meta brought 30,000 + 18,000 = 48,000 for 10,000 of spend. That is a return of 4.8, provided Meta’s own 30,000 is extra too. Without a test, the 18,000 could just as well be the season.

Not to be confused with

  • Incrementality — all the sales an ad adds, in any channel. The halo is the part that shows up in another channel’s report.
  • MER — total store revenue ÷ total marketing spend. It includes the halo but can’t show which channel caused it.

Right and wrong readings

  • Wrong: “Google Ads shows no conversions from Meta, so Meta does nothing for Google sales.” Right: Google Ads counts only Google ad interactions; a Meta ad seen before a Google search never appears there.
  • Wrong: “Brand searches grew after we started Meta, so the halo is proven.” Right: brand searches also grow when demand grows. Compare with regions or months without Meta.

Sources