Both seasonally adjusted and trend estimates are usually produced for key series from this survey.
Due to the disruption to earnings data, trend estimates were suspended during the COVID-19 period. During this period, the ABS also used forward seasonal factors to produce seasonally adjusted estimates for some AWE series. Forward factor adjustments are generally better suited to managing large movements at the end point of a series and ensure that large movements do not have a disproportionate influence on the seasonal factors.
From November 2022, the ABS reinstated the trend estimates and reverted to using the concurrent seasonal adjustment method. Due to the larger than usual point-to-point changes in May 2020 and November 2020 in particular, the ABS recommends caution when using trend estimates during this period.
Seasonal adjustment
Seasonal adjustment is a means of removing the estimated effects of normal seasonal variation from the series so that the effects of other influences can be more clearly recognised. Seasonal adjustment does not aim to remove the irregular or non-seasonal influences which may be present in any particular series. Influences that are volatile or unsystematic can still make it difficult to interpret the movement of the series even after adjustment for seasonal variation. If a time series has no identifiable seasonality it is not seasonally adjusted.
The AWE survey uses the concurrent seasonal adjustment technique to estimate seasonal factors, based on a synthesised quarterly original series. Linear interpolation is used to impute "missing" quarterly original observations based on the succeeding and preceding survey estimates. Under concurrent seasonal adjustment, the estimates of seasonal factors are improved as new or revised original estimates become available each period.
Trend estimates
Seasonally adjusted estimates can be smoothed to reduce the impact of irregular or non-seasonal influences. Smoothed seasonally adjusted series are called trend estimates.
The ABS considers that trend estimates provide a more reliable guide to the underlying direction of the original estimates and are more suitable than either the seasonally adjusted or original estimates for most business decisions and policy advice.
The trend estimates in the AWE survey are calculated using a centred 7-term Henderson moving average of the seasonally adjusted estimates of quarterly synthesised original data. Estimates for the three most recent periods cannot be calculated using this centred average method; instead an asymmetric average is used.
The changes to the moving average formulae can lead to revisions in the trend as data for subsequent periods becomes available. Revisions to the original data and re-estimation of seasonal adjustment factors also cause revisions to trend estimates. If a series is highly volatile then the trend estimates will be subject to greater revision for the latest few observations as new data become available. However, it is important to note that this does not make the trend series inferior to the seasonally adjusted or original series.
For further information, see A Guide to Interpreting Time Series - Monitoring Trends.