Price Indexes - General

The Bureau of Labor Statistics (BLS) prepares the Consumer Price Index for All Urban Consumers (CPI-U), and the Bureau of Economic Analysis prepares the Personal Consumption Expenditures (PCE) chain-type price index. Both indexes measure the prices paid by consumers for goods and services. Because the two indexes are based on different underlying concepts, they are constructed differently, and tend to behave differently over time. From the first quarter of 2002 through the second quarter of 2007, the CPI-U increased 0.4 percentage point per year faster than the PCE price index. This paper details and quantifies the differences in growth rates between the CPI-U and the PCE price index; it provides a quarterly reconciliation of growth rates for the 2002:Q1-2007:Q2 time period.

There are several factors that explain the differences in growth rates between the CPI and the PCE price index. First, the indexes are based on difference index-number formulas. The CPI-U is based on a Laspeyres index; the PCE price index is based on a Fisher-Ideal index. Second, the relative weights assigned to the detailed item prices in each index are different because they are based on different data sources. The weights used in the CPIU are based on a household survey, while the weights used in the PCE price index are based on business surveys. Third, there are scope differences between the two indexes—that is, there are items in the CPI-U that are out-of-scope of the PCE price index, and there are items in the PCE price index that are out-of-scope of the CPI-U. And finally, there are differences in the seasonal-adjustment routines and in the detailed price indexes used to construct the two indexes.

Over the 2002:Q1-2007:Q2 time period, this analysis finds that almost half of the 0.4 percentage point difference in growth rates between the CPI-U and the PCE price index was explained by differences in index-number formulas. After adjusting for formula differences, differences in relative weights—primarily “rent of shelter”—more than accounted for the remaining difference in growth rates. Net scope differences, in contrast, partly offset the effect of relative weight differences.
 

Foreign trade enables a nation to consume a different mix of goods and services than it produces, so to measure real gross domestic income (GDI) for an open economy, we must deflate by an index of the prices of the things that this income is used to buy, not the price index for GDP. The differences between these two indexes come from the export and import components of the GDP, and are measured by the trading gains index. Fisher indexes are a natural way to estimate the conceptual economic indexes of trading gains and real GDI because they are averages of the theoretical upper and lower bounds of the economic indexes. They can be decomposed in a way that permits analyses of the factors driving changes in trading gains, such as changes in the terms of trade and in the relative price of tradables, or changes in the prices of particular commodities. Applying these methods to the United States, we find that trading gains have a median absolute effect on US real GDI of 0.2 percentage points in annual data. The petroleum price shocks that occurred in late 1973 and in 1980 subtracted more than a full percentage point from the annual growth of real GDI, and in the first half of 2008 price increases in petroleum and other imported commodities subtracted 2 percentage points from the annual rate of growth of real GDI, making it negative despite the steady growth of real GDP. On the other hand, with petroleum prices excluded, US terms of trade begin to improve steadily starting in 1995 and the relative price of tradables falls. These effects increase the growth rate of US real GDI by 0.15 percent per year on average.