Cartoon explaining weighted CPI

[Jim__]

13. Yes quite.

According to the Bureau of Labor Statistics:

Traditionally, the CPI was considered an upper bound on a cost-of-living index in that the CPI did not reflect the changes in consumption patterns that consumers make in response to changes in relative prices.

Since January 1999, a geometric mean formula has been used to calculate most basic indexes within the CPI; this formula allows for a modest amount of substitution within item categories as relative price changes.

The geometric mean formula, though, does not account for consumer substitution taking place between CPI item categories. For example, pork and beef are two separate CPI item categories. If the price of pork increases while the price of beef does not, consumers might shift away from pork to beef. The C-CPI-U is designed to account for this type of consumer substitution between CPI item categories. In this example, the C-CPI-U would rise, but not by as much as an index that was based on fixed purchase patterns.

With the geometric mean formula in place to account for consumer substitution within item categories, and the C-CPI-U designed to account for consumer substitution between item categories, any remaining substitution bias would be quite small.

So, yes, just like beef is a different item category from pork, chicken is a different item category from rice and beans.