[citation needed] Total factor productivity (TFP) is often considered the primary contributor to GDP growth rate.
Since this cannot be measured directly the process of calculating derives TFP as the residual which accounts for effects on total output not caused by inputs.
[7] In 2001, William Easterly and Ross Levine estimated that for an average country the TFP accounts for 60 percent of growth of output per worker.
[9] Robert Ayres and Benjamin Warr have found that the model can be improved by using the efficiency of energy conversion, which roughly tracks technological progress.
Official statisticians tend to use the term "multifactor productivity" (MFP) instead of TFP because some inputs such as energy are usually not included.
[13][14][15][16] Growth accounting exercises and total factor productivity are open to the Cambridge critique.
Official statistics avoid measuring levels, instead constructing unitless growth rates of output and inputs and thus also for the residual.