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ANNUAL SEASONAL REANALYSIS
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 are then smoothed 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. These series can be used to better inform month-to-month comparisons.
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 reanalysis, the framework for estimating moving holidays and variable timing of the commencement of interviews in January is assessed for appropriateness. This is to ensure 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.
REMOVING THE EFFECT OF SUPPLEMENTARY SURVEYS
In common with similar countries (e.g. Canada), responses to the main Labour Force Survey are affected to some extent by the supplementary surveys conducted by the ABS in conjunction with the Labour Force Survey. The effects vary, depending on the topics covered by the supplementary surveys and their length. For many years, most of these supplementary surveys were run in the same month each year. As a result, any effects on the original Labour Force estimates caused by having different supplementary surveys in different months had been largely removed from the seasonally adjusted estimates by the seasonal adjustment process.
In late 2014, the ABS systematically assessed the effects of each supplementary survey on the seasonally adjusted Labour Force estimates, including aggregate monthly hours worked. Significant effects were found for some supplementary surveys, with little or no measurable impact caused by others. As a result of this analysis, an approach was developed to re-estimate the seasonality of the Labour Force data with specific adjustments made for the changed pattern of supplementary surveys. This approach was adopted for the October 2014 Labour Force release for most seasonally adjusted series, and the December 2014 Labour Force release for aggregate monthly hours worked.
Prior to the 2015 annual seasonal reanalysis, these adjustments were applied to Labour Force series (other than aggregate monthly hours worked) for the period December 2013 onwards only. These adjustments for the effect of supplementary surveys have now been applied, where necessary, to the entire time series from February 1978.
The independent technical review into the Labour Force Survey in 2014 recommended a review of aspects of the methodology adopted to account for the effects of supplementary surveys including:
In addition to the revisions due to the annual seasonal reanalysis, the adjustment for the February 2015 supplementary survey was re-estimated taking into account the additional observation for March 2015. This contributed to the impact, describe below, observed for the February 2015 data.
IMPACT ON THE LABOUR FORCE DATA
The overall impact of the annual seasonal reanalysis (including the revision described above to the adjustment for the February 2015 supplementary survey) on the Labour Force data for the period February 1978 to February 2015 was, for the most part, minimal.
The seasonally adjusted employed persons level series changed by an average absolute monthly value of 5,200 persons, with the largest revision of 60,300 persons occurring in July 1991. This revision is attributable to the adjustment to account for the changed timing of the Weekly Earnings of Employees supplementary survey which was conducted in July 1991 instead of the usual August month due to that year's Census of Population and Housing. Revisions include the impact of both the normal seasonal adjustment process and the results of the annual seasonal reanalysis. The employed persons trend series changed by an average absolute monthly value of 3,900 persons.
The unemployed persons seasonally adjusted level series for the period February 1978 to February 2015 changed by an average absolute monthly value of 1,800 persons, with the largest revision of 15,600 persons occurring in July 1983. The unemployed persons trend series changed by an average absolute monthly value of 1,200 persons.
For any queries regarding the annual seasonal reanalysis contact Labour Force Estimates on Canberra 02 6252 6525, or via email at email@example.com or Time Series Analysis Section on Canberra 02 6252 6345 or via email at firstname.lastname@example.org.
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