Now I've heard this disclaimer before but today I'm curious to the point of going to the bureau of labor statistics and visiting their frequently asked questions pull down.
My first question is why can't anyone write a clear sentence. Buellar? Buellar? Anyone?
So playing along here I did the FAQ thing and "asked":
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.
Wait wait there's more. This part is really choice and I am just going to copy and paste it without further comment. Just note a couple key phrases: "level of satisfaction" and "hamburger and steak are in different CPI item categories, so no substitution between them is built into the CPI-U or CPI-W"....!!
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.
There it is and there a lot more (sadly).