Amazon's annual Prime Day sale once again gave it its "biggest day ever" last week. But Sense360, a digital research firm, wanting to see what impact Amazon’s big numbers had on the foot traffic in its rivals' physical stores, decided to track shoppers who did and did not use the Amazon app.

The results showed a 7% drop in foot traffic during the Prime Day promotion among those who didn’t have the Amazon app and a 32% drop among those who did have the app. Sense360 tracked the behavior of 1.1 million shoppers who use a variety of apps from companies that partner with Sense360. Sense360 CEO Eli Portnoy wouldn’t identify those apps or say how many were used, beyond that it was “more than 50 and fewer than 100.”

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