The base period is usually understood to mean the period with which all the other periods are compared.

Three types of base period may be distinguished:

• the price reference period - the period that provides the prices to which the prices in other periods are compared. The prices of the price reference period appear in the denominators of the price relatives, or price ratios, used to calculate the index. The price reference period is typically

designated as period 0;

• the weight reference period - the period, usually one or more years, of which the expenditures serve as weights for the index.;

• the index reference period - the period for which the value of the index is set equal to 100.

Consumer price index manual: Theory and practice