We know that more people visited upscale grocery chain Whole Foods in the weeks after it became part of Amazon’s growing online and offline retail empire, but where did those people come from? Customer data shows that new visitors to Whole Foods stores were likely to be the wealthiest customers from competitors like Walmart, Costco, and Trader Joe’s.

This information comes from a report by the Thasos Group [PDF], a research firm that uses mobile phone location data to track how people move through the real world.

By harvesting location data from around 30 million mobile phones that belong to people who have opted in to share their location data with apps that they use, Thasos could track which shoppers were visiting Whole Foods for the first time, and where they had shopped before.

The company’s analysis found that new Whole Foods visitors had around the same household income as people who were already Whole Foods customers, $77,000. Most of them were already customers of Walmart (24%), Kroger-owned stores (16%), or Costco (15%).

Competitors that saw the biggest proportion of their regular customers check out Whole Foods during the weeks after the Amazon acquisition closed included Trader Joe’s (10%), Sprouts (8%), and Target (3%).

The large number of customers wandering over from Walmart are important, one retail expert notes, since the retailer has been expanding its selection of organic products, yet could lose its upper-income customers to Whole Foods.

“The data is a striking indication of the latent demand that exists for quality organics,” Kirthi Kalyanam, the director of the Retail Management Institute at Santa Clara University, told Bloomberg News. “Walmart is no doubt preparing to work extremely hard to overcome deep-set perceptions that its organics are of a lower quality than those found at Whole Foods.”

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