The weak performance of productivity since the crisis appears to stem mainly from weak business investment and low TFP growth. Weak business investment has resulted from weak demand and uncertainty about the pace of the recovery. TFP is equally important and has generally accounted for most of the variation in productivity over time, but is less well understood and so more difficult to forecast.
The second question – what will happen with productivity going forward – is the subject of intense debate. The range of forecasts is wide, and the historical record provides ample ground for humility.