Fisher Price Index

A number of different formulae, more than hundred, have been proposed as means of calculating price indexes. While price index formulae all use price and possibly quantity data, they aggregate these in different ways. A price index aggregates various combinations of base period prices (${\displaystyle p_{0}}$), later period prices (${\displaystyle p_{t}}$), base period quantities (${\displaystyle q_{0}}$), and later period quantities (${\displaystyle q_{t}}$). Price index numbers are usually defined either in terms of (actual or hypothetical) expenditures (expenditure = price * quantity) or as different weighted averages of price relatives (${\displaystyle p_{t}/p_{0}}$). These tell the relative change of the price in question. Two of the most commonly used price index formulae were defined by German economists and statisticians Étienne Laspeyres and Hermann Paasche, both around 1875 when investigating price changes in Germany.

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