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WHAT IF...? REVISIONS TO TREND ESTIMATES


EFFECT OF NEW SEASONALLY ADJUSTED ESTIMATES ON TREND ESTIMATES


TREND REVISIONS

Recent seasonally adjusted and trend estimates are likely to be revised when original estimates for subsequent months become available. The approximate effect of possible scenarios on trend estimates are presented below. Generally, the greater the volatility of the original series, the larger the size of the revisions to trend estimates. Analysis of the building approval original series has shown that they can be revised substantially. As a result, some months can elapse before turning points in the trend series are reliably identified.

The graphs and tables which follow present the effect of two possible scenarios on the previous trend estimates: that the April seasonally adjusted estimate is higher than the March estimate by 2.5% for the number of private sector houses approved and 15.1% for private sector dwellings excluding houses approved; and that the April seasonally adjusted estimate is lower than the March estimate by 2.5% for the number of private sector houses approved and 15.1% for private sector dwellings excluding houses approved. These percentages represent the average absolute monthly percentage change for these series over the last ten years.

APPROVED PRIVATE SECTOR HOUSES

WHAT IF NEXT MONTH'S SEASONALLY ADJUSTED ESTIMATE: Trend as published (1) rises by 2.5% on Mar 2018 (2) falls by 2.5% on Mar 2018 no. % change no. % change no. % change 2017 October 9 933 0.1 9 926 - 9 938 0.1 November 9 957 0.2 9 943 0.2 9 963 0.3 December 10 014 0.6 10 006 0.6 10 016 0.5 2018 January 10 091 0.8 10 110 1.0 10 084 0.7 February 10 175 0.8 10 235 1.2 10 148 0.6 March 10 254 0.8 10 364 1.3 10 202 0.5 - nil or rounded to zero (including null cells)

WHAT IF NEXT MONTH'S SEASONALLY ADJUSTED ESTIMATE: Trend as published (1) rises by 15.1% on Mar 2018 (2) falls by 15.1% on Mar 2018 no. % change no. % change no. % change 2017 October 8 849 - 8 830 -0.2 8 877 0.3 November 8 794 -0.6 8 764 -0.8 8 846 -0.3 December 8 745 -0.6 8 725 -0.4 8 766 -0.9 2018 January 8 712 -0.4 8 762 0.4 8 654 -1.3 February 8 683 -0.3 8 861 1.1 8 502 -1.8 March 8 663 -0.2 9 004 1.6 8 328 -2.0 - nil or rounded to zero (including null cells)