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15 A non-residential building is primarily intended for purposes other than long term residential purposes.
16 Alterations and additions refer to building activity carried out on existing building. It includes adding to or diminishing floor area, altering the structural design of a building and affixing rigid components which are integral to the functioning of the building.
17 The value of engineering work done for the private sector consists of the value of work done on prime contracts, plus speculative contracts, plus work done on own account.
18 The value of building and engineering work done during the period represents the estimated value of work actually carried out during the quarter on jobs which have commenced.
19 The ownership of a building is classified as either private sector or public sector, according to the sector of the intended owner of the completed building or project as evident at the time of approval.
20 Engineering projects are classified as either private sector or public sector according to the expected ownership of the project at the time of completion.
RELIABILITY OF THE ESTIMATES
21 The estimates of engineering activity in this publication are based on a sample survey as are the estimates of private sector building activity. A complete enumeration of public sector building activity is done. Because data are not collected for all engineering jobs nor for all building jobs, the published estimates are subject to sampling variability. Relative standard errors give a measure of this variability and therefore indicate the degree of confidence that can be attached to the data.
22 Relative standard errors for the value of work done in the March quarter 2002 are given below. There is 67% confidence that the actual value would be within one standard error of the sample estimate, and 95% confidence that it lies within two standard errors.
23 In the seasonally adjusted series, account has been taken of normal seasonal factors and the effect of movement in the date of Easter which may, in successive years, affect figures for different quarters.
24 Since seasonally adjusted statistics reflect both irregular and trend movements, an upward or downward movement in a seasonally adjusted series does not necessarily indicate a change of trend. Particular care should therefore be taken in interpreting individual quarter-to-quarter movements. In most instances, the seasonally adjusted components of a series add to the seasonally adjusted total. However, for Building Work Done, the 'Public' series shown in tables 1 and 3 has been seasonally adjusted independently. As a consequence, while the unadjusted components in the original series shown add to the totals, the adjusted 'Private' and 'Public' components of both 'Building Work Done' and 'Construction Work Done' may not add to the respective totals.
25 The seasonal factors are reviewed annually to take account of each additional year's data. The results of the latest review for Construction Work Done are reflected in the December quarter issue each year.
26 Seasonally adjusted series can be smoothed to reduce the impact of the irregular component in the adjusted series. This smoothed seasonally adjusted series is called a trend estimate.
27 The trend estimates are derived by applying a 7-term Henderson moving average to the seasonally adjusted series. The 7-term Henderson average (like all Henderson averages) is symmetric but, as the end of a time series is approached, asymmetric forms of the average are applied. Unlike weights of the standard 7-term Henderson moving average, the weights employed here have been tailored to suit the particular characteristics of individual series.
28 While the smoothing technique described in paragraphs 26 and 27 enables trend estimates to be produced for recent quarters, it does result in revisions to the estimates for the most recent three quarters as additional observations become available. There may also be revisions because of changes in the original data and as a result of the re-estimation of the seasonal factors. For further information, see Information Paper: A Guide to Interpreting Time Series - Monitoring Trends: an Overview (Cat. no. 1348.0) or contact the Assistant Director, Time Series Analysis on Canberra 02 6252 6076.
CHAIN VOLUME MEASURES
29 Chain volume estimates of the value of work done are presented in original, seasonally adjusted and trend terms.
30 While current price estimates of value of work done reflect both price and volume changes, chain volume estimates measure changes in value after the direct effects of price changes have been eliminated and therefore only reflect volume changes. The direct impact of the GST is a price change, and hence is removed from chain volume estimates. The deflators used to revalue the current price estimates in this publication are derived from the same price data underlying the deflators compiled for the dwellings and new other building components, and the new engineering construction component, of the national accounts aggregate 'Gross fixed capital formation'.
31 The chain volume measures of work done appearing in this publication are annually reweighted chain Laspeyres indexes referenced to current price values in a chosen reference year (currently 1999-2000). The reference year is updated annually in the June quarter publication. Each year's data in the value of work done series are based on the prices of the previous year, except for the quarters of the latest incomplete year which are based upon the current reference year (i.e. 1999-2000). Comparability with previous years is achieved by linking (or chaining) the series together to form a continuous time series. Further information on the nature and concepts of chain volume measures is contained in the ABS Information Paper: Introduction of Chain Volume Measures in the Australian National Accounts (Cat. no. 5248.0).
32 The factors used to seasonally adjust the chain volume series are identical to those used to adjust the corresponding current price series.
33 ABS publications draw extensively on information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated: without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.
34 Users may also wish to refer to the following publications which are available from ABS Bookshops:
Building Activity, Australia: Dwelling Unit Commencements, Preliminary (Cat. no. 8750.0) - issued quarterly
Building Activity, Australia (Cat. no. 8752.0) - issued quarterly
Building Approvals, Australia (Cat. no. 8731.0) -issued monthly
Private Sector Construction Industry, Australia, 1996-97 (Cat. no. 8772.0)
Engineering Construction Activity, Australia (Cat. no. 8762.0) - issued quarterly
House Price Indexes: Eight Capital Cities (Cat. no. 6416.0) - issued quarterly
Housing Finance for Owner Occupation, Australia (Cat. no. 5609.0) - issued monthly
Producer Price Indexes, Australia (Cat. no. 6427.0) - issued quarterly
35 Current publications and other products produced by the ABS are listed in the Catalogue of Publications and Products, Australia (Cat. no. 1101.0). The ABS also issues, on Tuesdays and Fridays, a Release Advice (Cat. no. 1105.0) which lists products to be released in the next few days. The Catalogue and Release Advice are available from any ABS office.
ABS DATA AVAILABLE ON REQUEST
36 As well as the statistics included in this and related publications, the ABS may have other relevant data available on request. Inquiries should be made to the National Information and Referral Service on 1300 135 070.
SYMBOLS AND OTHER USAGES
Where figures have been rounded, discrepancies may occur between sums of the component items and totals.
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