6401.0.55.003 - Seasonal Adjustment of Consumer Price Indexes, 2011  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 14/09/2011  First Issue
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1.1 The ABS first compiled the CPI in 1960 with series extending back to the September quarter 1948. The CPI measures quarterly changes in the price of a basket of goods and services, which accounts for a high proportion of expenditure by the CPI population group (i.e. metropolitan households). This basket covers a wide range of goods and services.

1.2 The movements in prices measured each quarter reflect a range of influences. Some users wish to focus on components or a subset of these influences. Analysts use a variety of measures, including seasonal adjustment, exclusion measures (eg. CPI excluding fuel) and statistical measures such as the Trimmed mean and Weighted median to undertake analysis of inflation in the Australian economy. Seasonal adjustment helps the analysis of price movements as it estimates and then removes influences that are systematic and calendar related from a time series.

1.3 The ABS produces two measures of underlying trend inflation, the Trimmed mean and Weighted median. In the 15th series these measures were calculated using a seasonal adjustment methodology developed by the RBA (Roberts, 2005). The 16th series CPI review recommended the ABS continue to produce analytical measures of underlying trend inflation, but replace the 15th series seasonal adjustment methodology with standard ABS seasonal adjustment methodology. This will ensure seasonally adjusted CPI data is consistent with other ABS data and results in more transparent and robust analytical series.

1.4 The following analytical measures will be published in the September quarter 2011 issue of Consumer Price Index, Australia (cat. no. 6401.0), scheduled for release on 26 October 2011:

    • All groups CPI, seasonally adjusted; comprises all components included in the All groups CPI, seasonally adjusted where seasonality has been identified at the weighted average of eight capital cities level.
    • CPI Expenditure classes, seasonally adjusted; comprises the subset of seasonally adjusted expenditure classes at the weighted average of eight capital cities level.
    • Trimmed mean and Weighted median; these are two analytical measures of underlying trend inflation. For more details see Chapter 5.