Common Misconceptions about the Consumer Price Index: Questions and Answers
An August 2008 Monthly Labor Review article by BLS economists John Greenlees and Robert McClelland reviews and analyzes some common misconceptions about the Consumer Price Index (CPI.) Those analyses are summarized here:
Has the BLS removed food or energy prices in its official measure of inflation?
No. The BLS publishes thousands of CPI indexes each month, including the headline All Items CPI for All Urban Consumers (CPI-U) and the CPI-U for All Items Less Food and Energy. The latter series, widely referred to as the "core" CPI, is closely watched by many economic analysts and policymakers under the belief that food and energy prices are volatile and are subject to price shocks that cannot be damped through monetary policy. However, all consumer goods and services, including food and energy, are represented in the headline CPI.
Most importantly, none of the prominent legislated uses of the CPI excludes food and energy. Social security and federal retirement benefits are updated each year for inflation by the All Items CPI for Urban Wage Earners and Clerical Workers (CPI-W). Individual income tax parameters and Treasury Inflation-Protected Securities (TIPS) returns are based on the All Items CPI-U.
The CPI used to include the value of a house in calculating inflation and now they use an estimate of what each house would rent for -- doesn't this switch simply lower the official inflation rate?
No. Until 1983, the CPI measure of homeowner cost was based largely on house prices. The long-recognized flaw of that approach was that owner-occupied housing combines both consumption and investment elements, and the CPI is designed to exclude investment items. The approach now used in the CPI, called rental equivalence, measures the value of shelter to owner-occupants as the amount they forgo by not renting out their homes.
The rental equivalence approach is grounded in economic theory, receives broad support from academic economists and each of the prominent panels, and agencies that have reviewed the CPI, and is the most commonly used method by countries in the Organization for Economic Cooperation and Development (OECD). Critics often assume that the BLS adopted rental equivalence in order to lower the measured rate of inflation. It is certainly true that an index based on home prices would be more volatile, and might move differently from other CPI indexes over any given time period. However, when it was first introduced, rental equivalence actually increased the rate of change of the CPI shelter index, and in the long run there is no evidence that the CPI method yields lower inflation rates than some other alternatives. For example, according to the National Association of Realtors, between 1983 and 2007 the monthly principal and interest payment required to purchase a median-priced existing home in the United States rose by 79 percent, much less than the rental equivalence increase of 140 percent over that same period.
When the cost of food rises, does the CPI assume that consumers switch to less desired foods, such as substituting hamburger for steak?
No. In January 1999, the BLS began using a geometric mean formula in the CPI that reflects the fact that consumers shift their purchases toward products that have fallen in relative price. Some critics charge that by reflecting consumer substitution the BLS is subtracting from the CPI a certain amount of inflation that consumers can "live with" by reducing their standard of living. This is incorrect: the CPI's objective is to calculate the change in the amount consumers need to spend to maintain a constant level of satisfaction.
Specifically, in constructing the "headline" CPI-U and CPI-W, the BLS is not assuming that consumers substitute hamburgers for steak. Substitution is only assumed to occur within basic CPI index categories, such as among types of ground beef in Chicago. Hamburger and steak are in different CPI item categories, so no substitution between them is built into the CPI-U or CPI-W.
Furthermore, the CPI doesn't implicitly assume that consumers always substitute toward the less desirable good. Within the beef steaks item category, for example, the assumption is that consumers on average would move up from flank steak to filet mignon if the price of flank steak rose by a greater amount (or fell by less) than filet mignon prices. If both types of beef steak rose in price by the same amount, the geometric mean would assume no substitution.
In using the geometric mean the BLS is following a recognized best practice for statistical agencies. The formula is widely used by statistical agencies around the world and is recommended by, for example, the International Monetary Fund and the Statistical Office of the European Communities.
Is the use of "hedonic quality adjustment" in the CPI simply a way of lowering the inflation rate?
No. The International Labour Office refers to the hedonic approach as "powerful, objective and scientific". Hedonic modeling is just one of many methods that the BLS uses to determine what portion of a price difference is viewed by consumers as reflecting quality differences. It refers to a statistical procedure in which the market valuation of a feature is estimated by comparing the prices of items with and without that feature. Then, for example, if a television in the CPI is replaced by one with a larger screen and higher price, the BLS can make an adjustment to the price difference by estimating what the old television would have cost had it had the larger screen size.
Many of the challenges in producing a CPI arise because the number and types of goods and services found in the market are constantly changing. If the CPI tried to maintain a fixed sample of products, that sample quickly would shrink and become unrepresentative of what consumers were purchasing. Each time that an item in the CPI sample permanently disappears from the shelves, the BLS has to choose another, and then has to make some determination about the relative qualities of the old and replacement item. If it did not--for example, if it treated all new items as identical to those they replaced -- significant upward or downward CPI biases would result.
Critics often incorrectly assume that BLS only adjusts for quality increases, not for decreases, and that hedonic adjustments have a large downward impact on the CPI. On the contrary, BLS has used hedonic models in the CPI shelter and apparel components for roughly two decades, and on average hedonic adjustments usually increase the rate of change of those indexes. Since 1998, hedonic models have been introduced in several other components, mostly consumer durables such as personal computers and televisions, but these newer areas have a combined weight of only about one percent in the CPI. A recent article by BLS economists estimated that the hedonic models currently used in the CPI outside of the shelter and apparel areas have increased the annual rate of change of the All Items CPI, but by only about 0.005 percent per year.
Has the BLS selected the methodological changes to the CPI over the last 30 years with the intent of lowering the reported rate of inflation?
No. The improvements chosen by the BLS that some critics construe to be a response to short term political pressure were, in fact, the result of analysis and recommendations made over a period of decades, and those changes are consistent with international standards for statistics. The methods continue to be reviewed by outside commissions and advisory panels, and they are widely used by statistical agencies of other nations.
Moreover, the sizes and effects of the changes implemented by the BLS are often over-estimated by critics. Some have argued that if the CPI were computed using the methods in place in the late 1970s, the index would now be growing at a rates as high as 11 or 12 percent per year. Those estimates are based on the belief that the use of a geometric mean index lowered the annual rate of change of the CPI by three percentage points per year, and a belief that other BLS changes, such as the use of hedonic models and rental equivalence, have lowered the growth rate of the CPI by four percentage points per year.
Neither belief is supported by evidence. BLS calculations have shown that the geometric mean formula has reduced the annual growth rate of the CPI by less than 0.3 percentage points. Hedonic quality adjustments for shelter regularly increase the rate of change of the CPI, and those for apparel have had both upward and downward impacts at different points in time and for different types of clothing. The BLS estimates that the overall impact of hedonic quality adjustments in use in other categories has been extremely small. Furthermore, if the CPI were using the pre-1983 asset-based method instead of rental equivalence to measure homeowner shelter cost it would yield a sharply lower current measure of shelter inflation, given that house prices are now declining in many parts of the country.
Does the Bureau of Labor Statistics calculate the CPI the same way as other nations? Do any differences in method keep the US CPI lower than the CPIs of those other nations?
Yes, the methods described above are used widely by nations in the OECD and the European Union. A recent report shows that rental equivalence is the most common method used to measure changes in the cost of shelter by the OECD -- with 13 of 30 nations employing it. The next most common method is for a nation to omit shelter from the CPI. The hedonic method of quality adjustment is used by at least 11 of the 29 other OECD nations, and five of the G-7 nations. Eurostat reports that the geometric mean is used by 20 of 30 countries for its Harmonized Indices of Consumer Prices.
Each nation's inflation experience is the result of its unique economic circumstances, so comparing the change in the U.S. CPI-U with inflation rates in other countries does not gauge the accuracy of U.S. inflation measures. Nevertheless, over the 1997-2007 period the U.S. CPI-U increased faster than the CPIs of 16 of the other 29 OECD nations, and faster than the CPIs of all of the other G-7 nations, including Canada, the United States' largest trading partner. Similarly, between the first quarters of 2007 and 2008 the U.S. CPI rose by more than the CPIs of 20 of the other 29 OECD nations and by more than any of the other G-7 nations, including Canada.
Find out more in "Addressing misconceptions about the Consumer Price Index" in the August 2008 Monthly Labor Review.
Last Modified Date: September 5, 2008