Current price estimates reflect both price and volume changes, and are published on a monthly basis. However, chain volume estimates, which are published on a quarterly basis (March, June, September and December publications), measure changes in value after the direct effects of price changes have been eliminated, and hence only reflect volume changes. The chain volume measures of the MHSI are annually reweighted chain Laspeyres indexes referenced to current price values in the chosen reference year. The indexes are linked using the one-quarter overlap method, and the reference year is currently 2022–23. Each financial year’s quarterly data in the MHSI chain volume series is based on the prices of the previous financial year, except for those quarters of the current financial year, which are based on the prices of the reference year. Comparability with previous years is achieved by linking (or chaining) the series together to form a continuous time series.
With each release of the September quarter issue of the MHSI publication, a new base year is introduced, and the reference year is advanced one year. This means that with the release of the September quarter 2025 issue of the MHSI publication, the chain volume measures for 2024–25 will have 2023–24 (the previous financial year) as their base year rather than 2022–23, and the reference year will be 2023–24. A change in the reference year changes levels but not growth rates for all periods. A change in the base year can result in revisions to growth rates for the last financial year.
Chain volume measures are not generally additive. In other words, component chain volume measures do not, in general, sum to a total in the way original current price components do. This means, for example, that the chain volume estimates for COICOP Divisions will not add to the total for Australia. To minimise the impact of this, the ABS uses the latest base year as the reference year. By adopting this approach, additivity does exist for the quarters following the reference year and non-additivity is relatively small for the quarters in the reference year and those immediately preceding it. Further information on the nature and concepts of chain volume measures is contained in the ABS publication Information Paper: Introduction of Chain Volume Measures in the Australian National Accounts (cat. no. 5248.0).