Spending by consumers accounts for 70% of overall economic activity, so the eight-week period encompassed by the SpendingPulse data is seen as a critical time not just for retailers but for manufacturers, wholesalers and companies at every other point along the supply chain.

The SpendingPulse data include sales by retailers in key holiday spending categories such as electronics, clothing, jewelry, luxury goods, furniture and other home goods between Oct. 28 and Dec. 24. They include sales across all payment methods, including cards, cash and checks.

It's the first major snapshot of retail sales during the holiday season through Christmas Eve. A clearer picture will emerge next week as retailers like Macy's ( M) and Target ( TGT) report revenue from stores open for at least a year. That sales measure is widely watched in the retail industry because it excludes revenue from stores that recently opened or closed, which can be volatile.

Despite the weak numbers out Tuesday, retailers still have some time to make up lost ground. The final week of December accounts for about 15% of the month's sales, said Michael McNamara, vice president for research and analysis at MasterCard Advisors SpendingPulse. As stores offer steeper discounts to clear some of their unsold inventory, they may be able to soften some of the grim results reflected in Tuesday's data.

Still, this season's weak sales could have repercussions for 2013, he said. Retailers will make fewer orders to restock their shelves, and discounts will hurt their profitability. Wholesalers, in turn, will buy fewer goods, and orders to factories for consumer goods will likely drop in the coming months.

In the run-up to Christmas, analysts blamed the weather and worries about the "fiscal cliff" for putting a damper on shopping. Superstorm Sandy battered the Northeast and mid-Atlantic states in late October. Many in the New York region were left without power, and people farther inland were buried under feet of snow. According to McNamara, the Northeast and mid-Atlantic account for 24% of U.S. retail sales.

Buying picked up in the second half of November as retailers offered more discounts and shoppers waylaid by the storm finally made it into malls, he said.

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