G.1 Measures of Consumer Price Inflation
The data under the ‘Consumer price index’ heading are from ABS Cat No 6401.0. Percentage changes are calculated from the indices published in ABS Cat No 6401.0. The following definitions apply from the September quarter 2000.
The ‘Consumer price index – All groups’ measure is the total or ‘headline’ consumer price index. The measure ‘Excluding volatile items’ is the CPI (all groups) less fruit, vegetables and automotive fuel.
The ‘Market prices excluding volatile items – goods’ component (formerly titled ‘Private-sector goods’) is the CPI (all groups – goods component) less fruit, vegetables, automotive fuel, utilities and pharmaceuticals.
The ‘Market prices excluding volatile items – services’ component (formerly titled ‘Private-sector services’) is the CPI (all groups – services component) less property rates and charges, health services, other motoring charges, urban transport fares, postal, education and child care.
The ‘Total’ measure of ‘Market prices excluding volatile items’ (formerly titled ‘Private-sector prices’) is the CPI (all groups) less fruit, vegetables, utilities, property rates and charges, health services, pharmaceuticals, automotive fuel, other motoring charges, urban transport fares, postal, education and child care.
The ‘Private consumption chain price index’ is sourced from ABS Cat No 5206.0.
The ‘Weighted median’ and ‘Trimmed mean’ are calculated using the component level data of the consumer price index. Both measures exclude interest charges prior to the September quarter 1998 and are adjusted for the tax changes of 1999–2000. The ‘Trimmed mean’ is calculated by ordering all the CPI components by their price change in the quarter and taking the expenditure-weighted average of the middle 70 per cent of these price changes. The ‘Weighted median’ is the price change in the middle of this ordered distribution, taking also expenditure weights into account. Annual rates of ‘Weighted median’ and ‘Trimmed mean’ inflation are calculated based on compounded quarterly rates. For calculating the ‘Weighted median’ and ‘Trimmed mean’, where CPI components are identified as having a seasonal pattern, quarterly price changes are estimated on a seasonally adjusted basis. Seasonal adjustment factors are calculated as concurrent factors, that is using the history of price changes up to and including the current CPI release. There is a series break at September 2002 due to the ABS publishing the ‘Weighted median’ and ‘Trimmed mean’ on behalf of the RBA from that point forward, using data to a higher level of precision than is publicly available.
For further information on the various measures of underlying consumer price inflation, refer to ‘Box D: Underlying Inflation’, Statement on Monetary Policy, May 2002; ‘Box D: Measures of Underlying Inflation’, Statement on Monetary Policy, August 2005; and Roberts (2005), ‘Underlying Inflation: Concepts, Measurement and Performance’, Reserve Bank of Australia Research Discussion Paper No 2005-05.