Editing Price index (section)

===== Fisher index =====
Named for [[Irving Fisher]], it’s the geometric mean of Laspeyres and Paasche:<ref>{{cite book |last1=Lapedes |first1=Daniel N. |url=https://archive.org/details/mcgrawhilldictio00iona/page/367 |title=Dictionary of Physics and Mathematics |publisher=McGrow–Hill |year=1978 |isbn=0-07-045480-9 |page=[https://archive.org/details/mcgrawhilldictio00iona/page/367 367]}}</ref>

: <math>P_F = \sqrt{P_L \cdot P_P}</math>

It balances Laspeyres’ base-period bias (overstating inflation) and Paasche’s current-period bias (understating it), offering greater accuracy than Marshall-Edgeworth’s arithmetic approach. It requires data from both periods, unlike unilateral indices, and in chaining, it multiplies geometric means of consecutive period-to-period indices.<ref>PPI manual, p. 610</ref>