8731.5 - Building Approvals, Western Australia, Sep 2003  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 07/11/2003  Ceased
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WHAT IF... ? REVISIONS TO TREND ESTIMATES


EFFECT OF NEW SEASONALLY ADJUSTED ESTIMATES ON TREND ESTIMATES

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.


TREND REVISIONS

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 October seasonally adjusted estimate is higher than the September estimate by 7% for the number of private sector houses approved and 7% for total dwelling units approved; and that the October seasonally adjusted estimate is lower than the September estimate by 7% for the number of private sector houses approved and 7% for total dwelling units approved. These percentages were chosen because they represent the average absolute monthly percentage change for these series over the last ten years.

PRIVATE SECTOR HOUSES
Graph - Private sector houses

WHAT IF NEXT MONTH’S SEASONALLY ADJUSTED ESTIMATE:
TREND AS PUBLISHED
1
2
rises by 7% on Sep 2003
falls by 7% on Sep 2003
no.
% change
no.
% change
no.
% change
May 2003
1,446
1.2
1,452
0.9
1,458
1.1
June 2003
1,468
1.5
1,470
1.3
1,473
1.0
July 2003
1,494
1.8
1,498
1.9
1,490
1.1
August 2003
1,520
1.7
1,529
2.1
1,500
0.7
September 2003
1,543
1.5
1,559
2.0
1,505
0.3
October 2003
n.y.a.
n.y.a.
1,587
1.8
1,505
0.1

TOTAL DWELLING UNITS
Graph - Total dwelling units

WHAT IF NEXT MONTH’S SEASONALLY ADJUSTED ESTIMATE:
TREND AS
1
2
PUBLISHED
rises by 7% on Sep 2003
falls by 7% on Sep 2003
no.
% change
no.
% change
no.
% change
May 2003
1,777
0.3
1,779
-0.4
1,789
-0.2
June 2003
1,796
1.1
1,787
0.4
1,791
0.2
July 2003
1,827
1.7
1,816
1.6
1,804
0.7
August 2003
1,860
1.8
1,856
2.2
1,817
0.7
September 2003
1,896
1.9
1,898
2.2
1,824
0.4
October 2003
n.y.a.
n.y.a.
1,940
2.2
1,828
0.3