The data sources and methods used in preparing ABS national accounts statistics are regularly reviewed and periodically changes are made to the basis of compilation of an item. A major methodological improvement to the Australian national accounts was the introduction of supply and use benchmarking and annually re-weighted volume estimates in 1998. The former results in greater coherence of the accounts and the latter provides a superior measure of economic growth to the previously available volume estimates based on 5 yearly reweighting.
Seasonal adjustment methods used by the ABS are based on the United States Bureau of the Census Method II Seasonal Adjustment program, X-11 variant. Traditionally, the national accounts seasonal factors were re-analysed each September quarter and factors were fixed for the rest of the year. From the September quarter 2006 issue of the national accounts, GDP and each of its components are concurrently adjusted for seasonality, although the results will still be reviewed each September quarter. This is expected to result in a quality improvement because the method is more responsive to emerging changes in seasonal patterns.