WASHINGTON (AP) -- The productivity of American workers rose in the October-December period but at a slower pace than the previous quarter. Growth in labor costs increased.

Productivity climbed at an annual rate of 1.3 percent in the fourth quarter, weaker than 3.5 percent productivity growth in the July-September period, the Labor Department reported Thursday. Labor costs rose at a 1.7 percent rate, up from a tiny 0.2 percent gain in the third quarter.

For the year, productivity rose a tiny 0.2 percent. It was the worst showing in five years. Productivity has slowed significantly in recent years for reasons that are unclear. It represents a worrisome trend given that growth in productivity is a key factor needed to boost living standards.

Productivity is the amount of output per hour of work. The fourth quarter slowdown had been expected given that overall economic growth, as measured by the gross domestic product, slowed in the fourth quarter. GDP grew at an annual rate of 1.9 percent in the final three months of the year, compared to a 3.5 percent gain in the third quarter.