Core Inflation: A Weighted Median Index - ARCHIVED

Core inflation should reflect what is basic in price movements and ignore temporary fluctuations that have no long-term impact on prices. The phenomenon of core inflation must be of a lasting nature. The targets were initially set on the basis of the overall consumer price index (CPI). However, the Bank of Canada has stated that for practical reasons, it will focus on the consumer price index excluding the volatile food and energy components.

The question that many are asking is the following: is a measure such as the CPI excluding food and energy a good indicator of core inflation? At the meeting of the 1996 Price Measurement Advisory Committee, a review of the literature on core inflation was presented. The Committee recommended taking a closer look at a weighted median index as a means of estimating core inflation. This study deals with the question of a weighted median index and covers the period of January 1985 to January 1997. The rates of change in the weighted median index calculated from monthly movements are quite often lower than the rates of change in the official index. This behaviour reflects the usual distribution of monthly price movements for the CPI, meaning a large proportion of the monthly movements are close to zero, and the remaining price movements are, in majority, positive. Because of this behaviour of monthly movements, the weighted median index advances much more slowly than the official index. This behaviour is just as evident when inflation advances at annual rates of 4% to 5% as when it ranges around 2%. An index based on the weighted median of monthly movements in the CPI yields somewhat disconcerting results. Even though some think that the official CPI does not clearly reflect the concept of core inflation, one does not necessarily expect to see such a large gap develop over time.