Solow Residual

The Solow residual is the portion of output growth that is not explained by the growth of measured inputs — capital and labour — after each input's growth is weighted by its share of national income. Introduced by Robert Solow in 1957, it is the empirical counterpart of total factor productivity (TFP) growth and is computed by subtraction rather than measured directly. Because it captures everything that raises output without raising measured inputs, it has been famously described as a 'measure of our ignorance': it labels what we cannot otherwise account for, lumping together genuine technical change, efficiency gains, and pure measurement error.