Answer: While both the PPI and CPI measure price change over time for a fixed set of goods and services, they differ in two critical areas: (1) the composition of the set of goods and services, and (2) the types of prices collected for the included goods and services.
The target set of goods and services included in the PPIs is the entire marketed output of U.S. producers. The set includes both goods and services purchased by other producers as inputs to their operations or as capital investment, as well as goods and services purchased by consumers either directly from the service producer or indirectly from a retailer. Because the PPI target is the output of U.S. producers, imports are excluded.
The target set of items included in the CPI is the set of goods and services purchased for consumption purposes by urban U.S. households. This set includes imports.
The price collected for an item included in the PPIs is the revenue received by its producer. Sales and excise taxes are not included in the price because they do not represent revenue to the producer. The price collected for an item included in the CPI is the out-of-pocket expenditure by a consumer for the item. Sales and excise taxes are included in the price because they are necessary expenditures by the consumer for the item.
The differences between the PPI and CPI are consistent with the different uses of the two measures. A primary use of the PPI is to deflate revenue streams in order to measure real growth in output. A primary use of the CPI is to adjust income and expenditure streams for changes in the cost of living.
The composition of items in the Finished Goods Price Index differs from that of the All Items Consumer Price Index in two major respects. First, the Finished Goods Price Index includes price changes for producers' durable equipment, which are not purchased by typical consumers and, therefore, are not included in the CPI. Second, the All Items CPI includes services which are not reflected in the Finished Goods Price Index. An additional difference is that the Finished Goods Price Index is only available at the U.S. level, while the All Items CPI is available at the regional, metropolitan area, and U.S. levels.