Less well-off consumers remained more frugal, most likely constrained by unemployment, declines in home values and the disappearance of easy credit. So the savings rate actually rose last year for those in middle-income brackets as they cut spending.

Job losses have disproportionately hit those at the lower end of the wage scale. According to the Labor Department, the unemployment rate among people in management, business or financial occupations was 4.8 percent in June, compared to 9.5 percent over all, 18.2 percent in construction and 12.1 percent in production.

As a result, the affluent generally maintained their spending power at a time when others were losing it. “High-income households drove the economy out of recession into recovery and powered the recovery through its first year,” Mr. Zandi concluded. He added that although the incomes of the richest people might have been affected by swings in dividend payments or bonuses, the change in their savings rate was most likely driven by increased spending.

Affluent spenders “began to come out of the bunker about this time last year,” Mr. Zandi said, “and part of it was related to the revival in the stock market.”

Other economists suggest that while Mr. Zandi’s conclusions make some sense, the data is hazy on the precise role that the rich have played in consumer spending. “We have tried to do other things like look at consumer expenditures on products mainly purchased by the rich and could never get anywhere,” said Barry P. Bosworth, a senior fellow at the Brookings Institution.

On the ground, those whose sales depend on affluent buyers have seen definite patterns. Last year and early this year, when the major stock gauges were rising, “everybody seemed to be a little bit more optimistic,” said Tom Hauswirth, general manager and partner of Moritz Cadillac, BMW and Mini in Arlington, Tex., near Dallas.

“Then I think everybody was affected when they saw the stock market go below 10,000,” he said. “Even though it may not affect their ability to buy or not, it affects their thinking.”