8226.0 - Electricity, Gas, Water and Sewerage Operations, Australia, 2004-05  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 13/10/2006   
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TECHNICAL NOTE 2 DATA RELIABILITY


ABS SURVEY DATA

1 For 2004-05, the utilities collection was, in part, a sample survey designed primarily to deliver estimates at the industry group level for Australia. State and territory estimates for ANZSIC Group 361 Electricity supply are also produced.



SAMPLE ERROR

2 The majority of data in this publication have been obtained from a sample of utilities industries businesses. As such, these data are subject to sampling variability; that is, they may differ from the figures that would have been produced if the data had been obtained from all utilities industries businesses in the population. The measure of the likely difference as used by the ABS is given by the standard error, which indicates the extent to which an estimate might have varied by chance because the data were obtained from only a sample of units. There are about two chances in three that a sample estimate will differ by less than one standard error from the figure that would have been obtained if the data had been obtained from all units, and about 19 chances in 20 that the difference will be less than two standard errors.


3 The standard error can also be expressed as a percentage of the estimate, and this is known as the relative standard error (RSE). RSEs at the industry group level for selected data items representing the full range of data contained in this publication are shown in Technical Note 3. Detailed RSEs can be made available on request.


4 Note that RSEs for ANZSIC Groups 361 Electricity supply and 362 Gas supply are generally very small: this is because the only sampled contribution to these estimates has been from BIT data. See Technical Note 1 paragraph 13 for details.


5 The size of the RSE may be a misleading indicator of the reliability of some of the estimates for trading profit, OPBT, EBIT and IVA. Estimates of these variables may legitimately include positive and negative values, reflecting the financial performance of individual businesses. In these cases, the aggregated estimate can be small relative to the contribution of individual businesses, resulting in a standard error which is large relative to the estimate.



NON-SAMPLE ERROR

6 All data presented in this publication are subject to non-sample error.


7 The imprecision due to sampling variability, which is measured by the standard error, should not be confused with inaccuracies that may occur because of inadequacies in available sources from which the population frame was compiled, imperfections in reporting by providers, errors made in collection such as in recording and coding data, and errors made in processing data. Inaccuracies of this kind are referred to collectively as non-sampling error and may occur in any enumeration, whether a full census or a sample.


8 Although it is not possible to quantify non-sampling error, every effort is made to reduce it to a minimum. Collection forms are designed to be easy to complete and assist businesses to report accurately. Efficient and effective operating procedures and systems are used to compile the statistics. The ABS compares data from different ABS (and non-ABS) sources relating to the one industry, to ensure consistency and coherence.