Is the difference between the CPI-U and the C-CPI-U expected to be fairly stable over time?
Earlier evidence suggested that the difference between the CPI-U and the C-CPI-U would be around 0.2 percent a year. For the period December 1999 to December 2000, however, the difference was 0.8 percentage point. There were a number of reasons for the larger difference, including the relative age of the weights in the CPI-U, and the increased variation in price movements across CPI item categories, causing the divergence between the CPI-U and C-CPI-U to grow. In each of the last four years (including 2004, for which the C-CPI-U values are not final), the difference in December-to-December changes was 0.3 or 0.4 percentage point.
