The Consumer Price Index is a measure of the change in the average price level of a fixed basket of goods and services purchased by consumers. Monthly changes in the CPI represent the rate of inflation for the consumer. Annual inflation is also closely watched.
The consumer price index is available nationally by expenditure category and by commodity and service group for all urban consumers (CPI-U) and wage earners (CPI-W). All urban consumers are a more inclusive group, representing about 87 percent of the population. The CPI-U is the more widely quoted of the two, although cost-of-living contracts for unions and Social Security benefits are usually tied to the CPI-W, because it has a longer history. Monthly variations between the two are slight.
The CPI is also available by size of city, by region of the country, for cross-classifications of regions and population-size classes, and for many metropolitan areas. The regional and city CPIs are often used in local contracts.
The Bureau of Labor Statistics also produces a chain-weighted index called the Chained CPI. This measures a variable basket of goods and services whereas the regular CPI-U and CPI-W measure a fixed basket of goods and services. The Chained CPI is similar to the personal consumption expenditure price index that is closely monitored by the Federal Reserve Board.