12.4 Números Índice
An index number is an average. (I. Fisher 1922, 4)
An index number (…) shows the average percentage change (…) from one point of time to another. (I. Fisher 1922, 3)
Referências
Fisher, Irving. 1922. The Making of Index Numbers: A Study of Their Varieties, Tests, and Reliability. 1. Houghton Mifflin Company. https://archive.org/details/makingindexnumb00fishgoog/mode/2up.