THE U.S. ECONOMY grew at a better-than-expected, but still sluggish, rate of 2 percent between July and September. Among the factors that contributed to growth were higher consumer spending and defense spending. Among the factors that retarded growth were a drop in net exports due to slowdowns in Europe and China, and — alarmingly — a 1.3 percent decline in non-housing business investment, the largest such quarterly drop since late 2009.