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1504.0 - Methodological News, Dec 2007  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 18/12/2007   
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Enhancing the ABS SEASABS Seasonal Adjustment System for Chained Volume Measures

The Australian Bureau of Statistics (ABS) publishes economic indicators as both current price values (CPVs or "nominal") and as chained volume measures (CVMs or "real"), which discount the impact of price changes. Both of these measures may be released to the general public via ABS publications in seasonally adjusted terms.

CPV seasonally adjusted estimates are both produced and quality assured by the ABS SEASABS seasonal adjustment system. The present system for seasonally adjusting CVMs involves transferring the appropriate seasonal factors and prior correction factors from ABS' seasonal adjustment package, SEASABS, to the FAME based National Accounts compilation/processing system.

This dual system is often operationally inefficient, complicated, less transparent and problematic. This is particularly the case when Subject Matter Areas (SMAs), other than National Accounts, produce seasonally adjusted CVMs for their own economic time series, because they have to synchronise the two systems with assistance from Time Series Analysis (TSA) Section for seasonal adjustment and from National Accounts Branch (NAB) for CVM support. For example, if any changes are made to the seasonal adjustment of CPVs, such as to the methods of adjustment, aggregation structures, parameter settings or prior corrections, this needs to be reflected in the FAME code that produces the corresponding seasonal adjusted CVMs, via manual updates to this code. This process is often problematic, especially in terms of synchronising the timing of these code changes with tight quarterly processing deadlines.

TSA, in conjunction with NAB and Statistical Information Technology Facilities Section (SITFS) have been developing an enhanced version of SEASABS, that has a demonstrated capability to reliably produce seasonally adjusted CVMs. With assistance from TSA (by constructing the CVM process structure in SEASABS), NAB staff have successfully trialled the enhanced SEASABS/CVM system on one of the most complicated structures in National Accounts - Inventories. The success of this trial paves the way for a new business model for SMA CVM processes/compilation, using only the SEASABS/CVM system.

TSA and SITFS staff are working together to enhance the SEASABS/CVM system by providing extra capabilities and flexibility to produce original CVMs, in addition to seasonally adjusted CPVs and seasonally adjusted CVMs estimates, in the same system. This new system will be released for testing in February 2008 and is expected to be released into production in April 2008.

Starting from early next year, TSA, NAB and SMAs will work together to begin to apply the new business model, in a production environment, to derive original CVMs, seasonally adjusted CPVs and seasonally adjusted CVMs estimates from the enhanced SEASABS/CVM system for a range of SMA clients.

For more information on this project, please contact Tom Outteridge on (02) 6252 6406 or Mark Zhang on (02) 6252 5132.


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