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Explanatory Notes
1 Introduction¶
This publication contains estimates of gross domestic product (GDP) and its components, components of state final demand, national and sectoral income accounts, the national capital account and supporting series. For the most part, these estimates are provided in trend and seasonally adjusted terms. Where trend and seasonally adjusted estimates are not available, original data are provided. Annual estimates, on an original basis, are also provided for the key aggregates. The list of time series spreadsheets (below) shows the full range of data provided.
2 Concepts, Sources and Methods
Australia's national accounts statistics are compiled in accordance with international standards contained in the System of National Accounts, 2008 (2008 SNA). Australia's application of these SNA standards is described in Australian System of National Accounts: Concepts, Sources and Methods. This publication outlines major concepts and definitions, describes sources of data and methods used to derive the full suite of national accounts estimates for Australia.
3 Gross Domestic Product
GDP is derived by three approaches: the income approach (I), the expenditure approach (E) and the production approach (P). A description of each approach is provided in the following paragraphs. While each measure should, conceptually, produce the same estimate of GDP, if the three measures are compiled independently using different data sources, then different estimates of GDP result.
4 Seasonally Adjusted Trend Estimates
The general methods for deriving seasonally adjusted and trend estimates are described in Australian System of National Accounts: Concepts, Sources and Methods.
4.1 Seasonal adjustment¶
Data that are affected by seasonal factors are adjusted to remove the effects of these factors. Three important points should be noted here:
The methods used in seasonal adjustment do not force the sum of the adjusted current price estimates for each quarter of a year to equal the original annual total. Where chain volume estimates have no apparent seasonality in their implicit price deflators, the estimates are adjusted using the corresponding factors for current price estimates. A special method, known as the pseudo-additive method, has been used to adjust the output of cereal crops. This is necessary to account for the fact that there is no cereal output in some quarters.
4.2 Trend estimates¶
A trend estimate is obtained by removing the irregular component from the seasonally adjusted series. For estimates in this publication, it is calculated using a centred 7-term Henderson moving average of the seasonally adjusted series. The procedure is designed to minimise distortions in the trend level, turning point shape and timing of turning points. Estimates for the three most recent quarters cannot be calculated using this centred average method; instead an asymmetric average is used. This can lead to revisions in the trend estimates for the last three quarters when data become available for later quarters, even if none of the original data for earlier quarters has changed.
The higher the 'irregular' component in a series, then the greater the likelihood that trend estimates for the latest quarters will be revised as more observations become available. However, it is important to note that this does not make the trend series inferior to the seasonally adjusted or original series. In fact, in such cases the effect of the irregular component on overall movements is likely to be even more in the seasonally adjusted and the original estimates than in the trend series.
Trend estimates for aggregates such as GDP are derived directly, rather than as the sum of components. As a result, the sum of the trend estimates of individual components of a particular aggregate will not sum to the overall trend estimate of the aggregate for the latest three quarters. This approach provides higher quality trend estimates for key aggregates, particularly GDP.
For more information about ABS procedures for deriving trend estimates and an analysis of the advantage of using them over alternative techniques for monitoring trends, see Information Paper: A Guide to Interpreting Time Series - Monitoring Trends or contact Time Series Analysis by email at time.series.analysis@abs.gov.au.