Törnqvist Index

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.