Bags can be misleading.

This weekend marks the traditional start to the holiday shopping season, and come Nov. 29 economists will be digesting a variety of data to help them assess how retailers will finish out the year. The number of shopping bags carried through parking lots the day after Thanksgiving may not be among them.

"We count bags, but you don't do it on Black Friday," advised Jack Kyser, senior economist at Los Angeles Economic Development Corp. "That's when retailers think they'll make a lot of money, so they do a lot of stunts and sales. But you have to go back the following week to really see how much people are buying."

In fact, Richard Giss said the day after Thanksgiving, known as Black Friday for its ability to thrust a retailer's bottom line into positive territory for the year, often presents a false start to the real spending season.

"There are lots of people in the mall, it's definitely busy, but I think people go out to look at what they want to buy, and buy later," said Giss, a partner in Deloitte & Touche's Los Angeles consumer business group.

"Looking at the weekend after Thanksgiving is very subjective, very anecdotal," Giss said. "We send a lot of people out to the malls to look at what crowds are like, when they form, what the parking lots are like. If people are circling around looking for a parking place, it's a good shopping day. If they find a place very easily, it's a bad shopping day."

One method that doesn't hold much water in Southern California is weather watching. In the Midwest and the East Coast, retailers run big sales on winter outerwear before and during the holidays. If it's unseasonably warm leading up to Christmas, Giss said, it can mean big losses as people do not buy heavy jackets and gloves.

"But looking at the weather in Southern California, it's a lame excuse unless we have a weekend with a huge downpour that will keep people away from stores," he said.

Giss actually starts his assessment earlier.

Back-to-school sales are an early, but useful gauge, Giss said, since the dollars that parents spend on kids' apparel and school supplies indicate how much money they have to spend generally. "If you have a dismal back-to-school period, it starts me on a cautious note," Giss said. (This year's results were mixed-to-sluggish.)

His team also takes into account unemployment statistics and uses pre-holiday customer surveys in addition to bag counts and parking lot surveys the day after Thanksgiving.

Aubie Goldenberg, a partner in the retail group at Ernst & Young, prefers hard data specifically fuel prices and how they affect shipping costs at big-box, low-price retailers. Also, if home equity loans and refinancings are up, it means lots of homeowners get infusions of money that can be spent on retail.

"We look at true economic data points, like interest rates and subjective things like consumer confidence, housing starts and unemployment," he said.

There is also some disagreement over the importance of this year's early Thanksgiving, which extends the holiday shopping period.

"The first thing economists look at is the number of days between Thanksgiving and Christmas, which is two more this year," Kyser said. "People feel happy about that. It gives them more time to shop."

But Goldenberg was less sure. "People will buy what they will buy," he said. "People will procrastinate, they always do, and the week before Christmas will still be a big week."

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