Washington - The National Retail Federation released some gloomy findings on Sunday about the start of the holiday shopping season: Total projected sales tumbled 11 percent to $50.9 billion during the long weekend compared with $57.4 billion last year, and a smaller share of consumers reported hitting the stores or shopping online.

A knee-jerk reaction to these numbers may be fear that retailers are not in for much Christmas cheer this year. But here are four reasons why it's too early to jump to that conclusion.

Analysts say the drop in sales likely reflects that holiday shopping is happening over a longer period, rather than that people are spending less overall. As we reported over the holiday weekend, Black Friday promotions have not only bled into Thanksgiving, they have spread out over the entire month of November. So by the time Black Thursday and Black Friday rolled around, plenty of shoppers had likely already pounced on Black Friday-worthy deals and didn't feel the need to shop. "We're just seeing a shifting of sales," said Frank Badillo, chief economist for Kantar Retail. "In the end, its a zero-sum game overall."

The Retail Federation has not adjusted its outlook for the entire holiday season. The NRF is sticking with its forecast of 4.1 percent sales growth for the full holiday season. Why? Because the industry group still believes that low gas prices and stronger economic fundamentals are going to boost spending over the next several weeks. Also, historical data show that the results of Black Friday weekend have little correlation with how sales stack up for the holiday season overall, so it would be imprudent to read too much into what happened over the four-day weekend.

"It's not to say that NRF is necessarily wrong," said Jim O'Sullivan, chief U.S. economist at High Frequency Economics. "It just hasn't been a very reliable indicator over time."

NRF's findings about online shopping are not consistent with other data released the weekend. NRF found spending online was nearly flat this year, a discouraging signal for retailers who plowed millions into improving their e-commerce experiences this holiday season. But plenty of other recent data tells a different story. IBM's real-time tracking index of digital shopping found that online sales on Thanksgiving were up 14.3 percent compared with 2013, while Black Friday online sales were up 9.5 percent. Online sales were up 17 percent on Saturday and Sunday, IBM said. Adobe found that consumers spent record amounts online Thursday and Friday - $1.3 billion on Thanksgiving and $2.4 billion the following day. Adobe's findings are based on an analysis of more than 350 million visits to 4,500 retail Web sites.

Wal-Mart, meanwhile, says that Thanksgiving Day, Black Friday and Saturday represented its all-time highest three-day stretch in online traffic and orders. Target reported that its offer of free shipping on all purchases through December 20th "continues to drive record-breaking online sales." And Visa reports that e-commerce sales from its U.S. account holders were up 17 percent on Thanksgiving compared to last year. On Black Friday, Visa account holders spent 18 percent more.

NRF's data is based on a survey, not store receipts. Think fast: How much did you spend in total on Christmas gifts this weekend? And how much of that was online versus in-store? I don't know about you, but I'm having a hard time calling up a precise number. And shoppers' memory of that data point is crucial to NRF's report. NRF's data comes from a survey of 4,631 shoppers conducted on Nov. 28 and 29. But there's an inherent squishy-ness to relying on consumers' own reporting of their spending over the holiday weekend. For truly concrete data, we'll have to wait until the Commerce Department releases its monthly retail sales report and retailers report their earnings reports for the fourth quarter.