Halo effects: when advertising one product lifts another

If you advertise the 20-ounce bottle, does the 12-pack sell more too? What about the brand's other flavors, or a product in a completely different category? When advertising for one product appears to lift sales of another, marketers call it a halo effect. It's a real phenomenon in some cases. It's also one of the most frequently overclaimed results in retail media reporting.

The word "appears" is doing a lot of work. Here's how to check whether a halo is there.

What is a halo effect in advertising?

The term comes from psychology, where the halo effect describes how a positive impression in one area spills over into others. In advertising, it usually means that promoting one product benefits related products that weren't directly advertised.

There are a few versions. A brand halo is when an ad for one item lifts other items from the same brand. A category halo is when advertising lifts the whole category, including competitors. A cross-category halo is when an ad for one product lifts sales of something shoppers buy with it, such as salsa alongside chips.

Each is plausible in principle. Each needs evidence before it goes in a report.

How do you look for a halo in store-level data?

The same way you look for any campaign effect: compare advertised stores with similar stores that weren't advertised, over the same period. But instead of looking only at the advertised product, look at the related products too.

A hypothetical: a campaign promotes a brand's 20-ounce bottle in 150 stores. Compared with 150 similar stores, the advertised bottle sells more during the flight. The brand's 12-pack, which wasn't advertised, also sells a bit more in the advertised stores. That's a possible brand halo.

Store-level scan data, like the data analyzed by NRS Insights, makes this kind of product-by-product comparison possible, since it records sales by item and store.

Define the related products before the campaign. Deciding afterward which products to check invites finding a halo by searching until something moves.

What can create a false halo?

Season. If the campaign ran in summer and both products are cold drinks, both will rise in advertised and comparison stores alike. That's why the comparison group matters.

Promotions. If the unadvertised product had a price cut during the same weeks, its rise may be the price, not the halo.

Distribution changes. If the related product gained shelf space in the advertised stores, more sales could reflect availability.

Chance. Look at enough related products and one of them will rise by chance. If you checked twenty products and one moved, that's weak evidence.

Differences between store groups. If the advertised stores were already trending up for the brand before the campaign, a halo can appear where there's only a pre-existing trend.

How should a halo be reported?

Separately from the main effect. Report the advertised product's result first, then any halo, clearly labeled.

With the same rigor. A halo claim should meet the same standard as the main result: a fair comparison, a stated range and a note on what else could explain it.

With restraint. If the evidence is thin, say it's suggestive, not established. A report that claims halos on every campaign will lose credibility quickly. To discuss campaign measurement, contact the NRS Digital Media team, or visit the NRS Digital Media site.