4 The use of sample survey techniques in the Building Activity Survey means that reliable estimates of the number of dwelling commencements are generally available only at state, territory and Australia levels. Although subject to higher relative standard errors, a range of sub-state estimates of dwelling commencements may be available. Detailed data on Building Approvals, based on information reported by local government and other reporting authorities, are available for regions below state and territory level from Building Approvals, Australia (cat. no. 8731.0).
6 Building jobs (and their related dwellings) are classified both by the Type of Building (i.e. 'house', 'other residential building') and by the Type of Work involved (i.e. 'new' and 'conversions, etc.'). These classifications are used in conjunction with each other and their categories are defined in the Glossary.
7 Since the estimates are based on a sample of approved residential building jobs, the estimates of commencements of dwellings and total dwellings 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.
8 Estimated relative standard errors for the number of dwellings commenced in the June quarter 2012 are given below. There is 67% confidence that the actual number would be within one standard error of the sample estimate, and 95% confidence that it lies within two standard errors.
Relative Standard Errors, June quarter 2012
9 In addition, some returns containing jobs not known to have commenced are not received in time for inclusion in these estimates. Allowance is made for a proportion of these jobs, based on past experience, likely to have commenced. Estimates in this issue for the last two quarters are therefore subject to revision.
14 As a general rule, caution should be used when using the seasonally adjusted series for dwelling unit commencements in Northern Territory and Australian Capital Territory. The small numbers and volatile nature of these data makes reliable estimation of the seasonal pattern very difficult.
15 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 series.
19 All tables in this publication are available in electronic form on the ABS web site.