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 February seasonally adjusted estimate is higher than the January estimate by 3.8% for the number of private sector houses approved and 13% for private sector other dwelling units approved; and that the February seasonally adjusted estimate is lower than the January estimate by 3.8% for the number of private sector houses approved and 13% for private sector other dwelling units approved. These percentages represent the average absolute monthly percentage change for these series over the last ten years.
PRIVATE SECTOR HOUSES APPROVED
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| | | | WHAT IF NEXT MONTH‘S SEASONALLY ADJUSTED ESTIMATE: |
| | TREND AS PUBLISHED | (1) rises by 3.8% on Feb 2007 | (2) falls by 3.8% on Feb 2007 |
| | no. | % change | no. | % change | no. | % change |
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| 2006 | | | | | | |
| September | 8 918 | -0.1 | 8 917 | -0.1 | 8 928 | 0.1 |
| October | 8 838 | -0.9 | 8 834 | -0.9 | 8 855 | -0.8 |
| November | 8 712 | -1.4 | 8 709 | -1.4 | 8 719 | -1.5 |
| December | 8 569 | -1.6 | 8 578 | -1.5 | 8 551 | -1.9 |
| 2007 | | | | | | |
| January | 8 434 | -1.6 | 8 480 | -1.1 | 8 391 | -1.9 |
| February | 8 318 | -1.4 | 8 417 | -0.7 | 8 250 | -1.7 |
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PRIVATE SECTOR OTHER DWELLINGS
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| | | | WHAT IF NEXT MONTH'S SEASONALLY ADJUSTED ESTIMATE: |
| | TREND AS PUBLISHED | (1) rises by 13% on Feb 2007 | (2) falls by 13% on Feb 2007 |
| | no. | % change | no. | % change | no. | % change |
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| 2006 | | | | | | |
| September | 3 677 | -4.6 | 3 658 | -5.1 | 3 681 | -4.5 |
| October | 3 535 | -3.9 | 3 498 | -4.4 | 3 538 | -3.9 |
| November | 3 491 | -1.2 | 3 470 | -0.8 | 3 490 | -1.4 |
| December | 3 543 | 1.5 | 3 599 | 3.7 | 3 547 | 1.6 |
| 2007 | | | | | | |
| January | 3 631 | 2.5 | 3 810 | 5.9 | 3 637 | 2.5 |
| February | 3 798 | 4.6 | 4 058 | 6.5 | 3 731 | 2.6 |
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