A statistic which assigns a single number to several individual statistics in order to quantify trends. The best-known index in the United States is the consumer price index, which gives a sort of ``average'' value for inflation based on the price changes for a group of selected products.

Let be the price per unit in period , be the quantity produced in period , and be the value of the units. Let be the estimated relative importance of a product. There are several types of indices defined, among them those listed in the following table.

Index | Abbr. | Formula |

Bowley Index | ||

Fisher Index | ||

Geometric Mean Index | ||

Harmonic Mean Index | ||

Laspeyres' Index | ||

Marshall-Edgeworth Index | ||

Mitchell Index | ||

Paasche's Index | ||

Walsh Index |

**References**

Fisher, I. *The Making of Index Numbers: A Study of Their Varieties, Tests and Reliability, 3rd ed.*
New York: Augustus M. Kelly, 1967.

Kenney, J. F. and Keeping, E. S. ``Index Numbers.'' Ch. 5 in
*Mathematics of Statistics, Pt. 1, 3rd ed.* Princeton, NJ: Van Nostrand, pp. 64-74, 1962.

Mudgett, B. D. *Index Numbers.* New York: Wiley, 1951.

© 1996-9

1999-05-26