The U.S. economy grew at a 3.2 per cent annual rate in the October-December quarter on the strength of the strongest consumer spending in three years, an encouraging sign for 2014. The fourth-quarter increase followed a 4.1 per cent growth rate in the July-September quarter, when the economy benefited from a buildup in business stockpiles. For 2013 as a whole, the economy grew a tepid 1.9 per cent, weaker than the 2.8 per cent increase in 2012, the Commerce Department said on Thursday.