Real gross domestic product -the output of goods and services produced by labor and property in the U.S. -increased at an annual rate of 3.8% in the second quarter of 2007, according to final estimates released by the Bureau of Economic Analysis. In the first quarter, real GDP increased 0.6%.   ; These GDP estimates are based on more complete source data than were available for  ; the preliminary estimates issued last month. In the preliminary estimates, the increase in real GDP was 4%.   ; The acceleration in real GDP growth in the second quarter primarily reflected a downturn in imports, upturns in federal government spending and in private inventory investment, accelerations in exports, in nonresidential structures, and in equipment and software, and a smaller decrease in residential fixed investment.