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ANNUAL SEASONAL RE-ANALYSIS
Systematic and calendar related influences which have the same timing, same direction and similar magnitude every year, are removed to create the seasonally adjusted series. The presence and size of influences due to moving holidays, the variable timing of the commencement of interviews in January and the timing of supplementary surveys are estimated using a regression-ARIMA framework and also removed. The regression-ARIMA framework enables these influences to be accurately estimated. Without accurate estimation of these effects, the seasonal pattern may be obscured, and the seasonal factors may be less accurate.
The seasonally adjusted series irregular component is removed to create the trend series. Seasonally adjusted and trend series are revised each month to take account of the latest original estimates.
The ABS aims to produce high quality seasonally adjusted estimates that are without systematic related variation.
Seasonally adjusted aggregate hours worked estimates include more extensive corrections for the influence of public holiday and school holiday effects. Each moving holiday is estimated and removed in the aggregate state/territory estimates. State/territory level influences are used to estimate the school and public holiday effects in the Australia and full-time/part-time by sex estimates.
During each annual seasonal re-analysis, the framework for estimating moving holidays and variable timing of the commencement of interviews in January is assessed for appropriateness. This ensures that the impact of these influences are being appropriately estimated from year to year, that assumptions used in the regression-ARIMA framework continue to be valid, and to implement improvements in estimation methodology.
CHANGES TO THE SEASONAL FILTER LENGTHS
As part of ongoing continuous improvement, the ABS has completed a review of the length of seasonal filters used in the Labour Force series. This review determined that changes to the lengths of seasonal filters for specific seasonally adjusted series would provide more stable seasonal factors and reduce the average size of revisions through the concurrent seasonal adjustment and trend estimation process.
The ABS has changed the filter lengths for the series listed below, which has resulted in minor one-off revisions to the time series in the March 2017 estimates, beyond that usually observed through the annual seasonal re-analysis process.
It is important to note that Labour Force series follow an 'aggregation structure', which means that improvements in component series will flow through to the higher level series. For example, an improved filter length for the 'Employed, Australia, Males, Part-time' series will lead to minor improvements to its higher level aggregate series - 'Employed, Australia, Males'.
IMPACT ON THE LABOUR FORCE DATA
To account for the changes made to the supplementary survey program from 2014, the seasonal adjustment parameters and prior corrections have been monitored and revised regularly on an ongoing basis. As a result, revisions to seasonally adjusted and trend estimates arising from the 2017 annual seasonal re-analysis have been minimal.
ONGOING REVIEW OF METHODOLOGY
As part of a process of continuous improvement, the ABS will continue to explore options for further improving the quality of Labour Force time series. Such investigations may identify further optimisations.
The ABS will continue to provide updates on any developments in this space within Labour Force, Australia (cat. no. 6202.0), ahead of any changes being implemented as part of the 2018 annual seasonal re-analysis.
For any queries regarding the implementation of these changes contact the National Information Referral Service on 1300 135 070, or via e-mail at firstname.lastname@example.org.
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