Wal-Mart Stores Inc has agreed to give its U.S. store data to Nielsen Holdings NV , bolstering an industry benchmark that has long lacked insights into sales at the world's largest chain.

Nielsen gathers and analyzes sales information from a variety of U.S. chain stores, giving manufacturers, Wall Street analysts and others a glimpse at how products such as food and detergent are selling -- everywhere from grocery stores such as Kroger Co to mass merchants such as Target Corp

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However, Wal-Mart's U.S. discount stores had not shared its data in more than a decade, which meant that Nielsen's widely used metrics were missing the country's largest retailer in terms of revenue.

Walmart and Sam's Club stores will now report their sales information to Nielsen, and Nielsen will become Walmart's primary provider for market information, tools and training, the companies said in a joint announcement on Thursday.

The move comes after Wal-Mart in February named Sam's Club executive Cindy Davis as the executive vice president of Walmart global customer insights, a new team that is studying customer trends.

(Reporting by Jessica Wohl, editing by Maureen Bavdek)

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