WASHINGTON (AP) — U.S. productivity fell at an annual rate of 4.2% in the fourth quarter, the largest quarterly decline in nearly four decades. That revised figure released by the Labor Department on Thursday is slightly smaller than the 4.7% decline estimated a month ago. But it was still the biggest drop since the second quarter of 1981. Productivity is the amount of output per hour of work. The revised figure released by the Labor Department Thursday was slightly smaller than the 4.7% decline estimated a month ago. But it was still the biggest drop since the second quarter of 1981, when productivity fell at a rate of 5.1%.