Cyclical forces probably played some role. After September 11, many businesses sharply reduced their payrolls in anticipation of a slump in demand. But demand continued to grow briskly, and these companies learned to squeeze more output out of a smaller workforce. These efficiency gains likely were facilitated by the capital investments of recent years.
Adjusting to new technologies takes time, and it is plausible that such an adjustment process has continued to boost productivity growth in recent years. Although cyclical forces and lags in the assimilation of new technologies have been important, their influence is likely to be transitory.