Improving the Seasonal Adjustment of Coal exports
The ABS publishes a variety of externally sourced statistics on exports and imports.
Seasonal adjustment removes the impact of systematic effects observed in sub annual statistics, such as those caused by the influence of weather, financial reporting conventions and social traditions. Quarterly exports and imports volumes are also published in seasonally adjusted terms, by first removing the impact of price changes from the collected current price values, then seasonally adjusting the resulting "real" or volume statistics.
In most cases, when the price is not influenced by seasonality, the same seasonal adjustment factors can be applied to values and to their corresponding volumes. This had been the method used for Coal exports, until the March 2011 reference quarter. However, following discussions with a major user of these statistics, the ABS introduced an independent seasonal adjustment for Coal export volumes, along with other mining commodities such as metal ores, other mineral fuels (including LNG) and for the imports of fuels and lubricants. This independent seasonal adjustment of volumes better takes into account the influence of systematic (seasonal) variation in the prices of these commodities. In particular for coal export volumes, this has greatly improved the quality of the published seasonally adjusted measure, in response to the users.
The improved seasonal adjustment methodology has been implemented for all periods after September Quarter 2005 inclusive. Application of the revised methodology throughout the entire time series is currently under investigation.
For more information on the publication of exports and imports, please contact Selvi Sekhar on 02 6252 5540 or for more information on seasonal adjustment, please contact Lisa Apted (03 6222 5932 or lisa.apted@abs.gov.au) or Tom Outteridge (02 6252 6406 or tom.outteridge@abs.gov.au).
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