CHICAGO — Shoppers who endured long lines and sometimes-frigid temperatures spent only slightly more during their Black Friday shopping sprees than they did last year, according to data released yesterday by a research firm.

At the same time, their pajama-clad counterparts, a much smaller group that accounted for only a fraction of overall sales, shopped online from the warmth of their homes and dramatically boosted their spending.

More than a year after the economy's collapse began rattling shoppers, industry observers said Friday's shopping sprees offered a strong start to the holiday season.

"We have struggled for a long time, and one of the ways for the economy to get going again is for the consumer to begin to spend more freely," said Bill Martin, co-founder of research firm ShopperTrak, which released its sales figures yesterday. "And I think this is an indication they were willing to do that."

Preliminary sales data from Martin's organization, a Chicago research firm that tracks sales at more than 50,000 stores, showed shoppers spent $10.66 billion when they hit the malls on the day after Thanksgiving. That's only 0.5 percent more than last year, when Black Friday sales rose a striking 3 percent.

The traditional shopping spree — dubbed Black Friday because it often was the day when a surge of shoppers helped stores break into "the black," or profitability, the full year — has marked the kickoff of holiday shopping for many consumers.

But its importance has faded in recent years as merchants started hawking the deep discounts usually reserved for that day well in advance.

For example, last year's Black Friday spending grew from $10.3 billion to about $10.6 billion. But the overall holiday spending fell 4.4 percent as shoppers slowed spending as the holiday season went on.

Still, the day is often used as an important barometer of shoppers' mindset: what kinds of items they're buying and what kind of discounts will lure them.

On Friday, many of the in-store deals were also available online, causing some Web sites to overload as shoppers tried to get deals without waiting in long, cold lines.

Steve Segal, a 47-year-old attorney from Bridgewater, N.J., avoided the midnight crowds on Black Friday as he searched for a hair straightener for his daughter. But his shopping was derailed when the item was out of stock in stores and Kohl's Web site was overwhelmed by a crush of shoppers.

He wound up buying it elsewhere online — for a cheaper price and with free shopping. "It was a vicious cyber-circle," he said.

Web marketing analyst Coremetrics said its data showed the average amount online shoppers spent on Black Friday rose 35 percent as shoppers spent roughly $170.19 per order — up from $126.04 last year.

The company, based in San Mateo, Calif., also said Web shoppers also bought more items each time they checked out from an online merchant, snagging about 5.4 items in their carts, up from 4.6 last year. Overall, Web sales account for about roughly 7 percent of overall retail sales, according to Forrester Research.

Shop-by-television sales were also strong at the shopping network QVC, which said its Black Friday sales totaled $32 million — up almost 60 percent from last year, thanks to its first push to promote its post-Thanksgiving deals.