Experts on retail sales are obsessed with Thanksgiving weekend _ particularly the Black Friday shopping frenzy. That's especially true this year, as analysts look to the traditional start of the holiday shopping season for clues about how strongly the economy will rebound from the worst recession since the 1930s.

Most pundits generally agree that the start of the season was just ho-hum. But if you examine the details, you'll come across all sorts of disagreement over exactly how things have gone.

Why is it so hard to judge how many shoppers turned out, and how much they spent?

Here are some questions and answers.

Q: How important is Thanksgiving weekend as a predictor of the holiday shopping season?

A: The day after Thanksgiving is the traditional start of the season, and many stores have expanded the number of early morning specials and hours to get shoppers revved up.

In recent years, Black Friday has been the busiest shopping day of the year. But it's not considered a predictor of the rest of the holiday season, since it accounts for about 10 percent of total holiday sales.

Still, pundits study the weekend's receipts to decipher shoppers' mindsets. And if stores have a weak start to the season, chances are slim that they will be able to make up for lost sales.

Q: What makes this season's kickoff particularly hard to assess?

A: One major factor is that stores have increasingly been hawking deals and offering expanded hours throughout November in hopes of getting shoppers to do their holiday buying earlier. That has likely diluted sales for the holiday weekend.

Parsing the data got even trickier as many stores blurred their Web and land-based businesses in an effort to generate more sales on Black Friday. For the first time, major merchants including J.C. Penney Co. and Sears Holdings Corp. offered early morning Black Friday specials on their Web sites at the same time as in their stores, as they aimed to compete with pure online retailers.

That helped boost online sales on Thursday and Friday, which rose 11 percent, compared with the same period a year ago, according to comScore Inc., an Internet research company.

Also, more stores, like Old Navy, were open on Thanksgiving.

"Black Friday was definitely expanded. It wasn't as concentrated," said Bill Lewis, executive vice president of Karabus Management, a retail advisory firm. He noted that heavy online buying this past weekend likely depressed store traffic.

Such heavy online buying will not be reflected in sales at stores opened at least a year _ numbers that are being reported by major retailers on Thursday. Most figures exclude online sales.