The Commerce Department said Thursday it made a mistake in calculating Americans' personal income in March. Income went up, though not as much as the government had said.

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Personal income, which includes government payments as well as wages, rose by 0.5 percent in March from the previous month, the department's Bureau of Economic Analysis now says. On Monday, the government put the increase at 0.8 percent.

The mistake involved the treatment of payments related to the new Medicare prescription drug plan.

The payments had the effect of boosting overall income for March and should not have been included in the March report. They are supposed to be logged for April, the bureau said.

The mistake did not affect the calculation of gross domestic product for the January-to-March quarter. GDP — the value of all goods and services produced in the United States, rose at a 4.8 percent pace in the first quarter, the best showing in 2 1/2 years.

Economists said the new income figure does not alter their assessment of where the economy is heading. Analysts expect growth to slow to about 3 percent, still a healthy pace — in the April-to-June quarter.

Income growth is the power of future spending by consumers.

"A 0.5 percent increase in incomes is still a strong pace and should fuel incomes down the road," said Richard Yamarone, economist at Argus Research.

In March, consumer spending rose by 0.6 percent, the government reported Monday. That marked an improvement from February's 0.2 percent increase. The bureau's mistake did not affect its estimates on spending.

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