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	Solow Residual	Törnqvist Index
Field	Economics	Economics
Family	Regression model	Process / pipeline
Year of origin	1957	1936
Originator	Robert Solow	Leo Törnqvist; superlative theory by W. Erwin Diewert
Type	Residual measure of total factor productivity growth	Superlative index number for aggregating prices or quantities
Seminal source	Solow, R. M. (1957). Technical change and the aggregate production function. The Review of Economics and Statistics, 39(3), 312–320.	Diewert, W. E. (1976). Exact and superlative index numbers. Journal of Econometrics, 4(2), 115–145.
Aliases	TFP Residual, Measure of Our Ignorance, Technical Change Residual, Multifactor Productivity Residual	Tornqvist Index, Tornqvist-Theil Index, Translog Index, Tornqvist Price Index
Related	3	3
Summary	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.	The Törnqvist index is a superlative index number used to aggregate many individual prices or quantities into a single measure of overall price change or quantity change between two periods. It is a weighted geometric mean of the individual price (or quantity) relatives, where each item's weight is the average of its value shares in the two periods. Because it is 'exact' for the flexible translog aggregator function, it is the standard tool for constructing productivity indices and is widely used in national accounts, productivity statistics, and price measurement.