Underlying Inflation: Concepts, Measurement and Performance

This paper explores the concept of underlying inflation and the properties of various measures of underlying inflation in the Australian context. Underlying inflation measures are routinely calculated and monitored by central banks in many countries, including the Reserve Bank of Australia. Alternative measurement concepts are explored, and a range of measures that have been calculated for Australia are discussed and evaluated on the basis of statistical criteria. These criteria capture the intuition that a good measure of underlying inflation should be less volatile than CPI (or headline) inflation, be unbiased with respect to CPI inflation, and capture the ‘trend’ in CPI inflation so that, on average, CPI inflation will tend to adjust towards the measure of underlying inflation. In the Australian context, statistical measures of underlying inflation, such as the trimmed mean or weighted median, perform fairly satisfactorily against these criteria. The performance of these measures can be further improved by seasonally adjusting prices at the CPI component level. Although underlying inflation measures have become less necessary in the past decade as inflation itself has become less volatile, these findings suggest that underlying inflation measures can still add value to the analysis of inflationary trends.