TECHNICAL NOTE 1: SAMPLING VARIABILITY
1 Since the estimates in this publication are based on information obtained from a sample drawn from units in the surveyed population, the estimates are subject to sampling variability. That is, they may differ from the figures that would have been produced if all units had been included in the survey.
2 One measure of the likely difference is given by the standard error (SE), which indicates the extent to which an estimate might have varied by chance because only a sample of units was included. The relative standard error (RSE) provides an immediate indication of the percentage errors likely to have occurred due to sampling, and thus avoids the need to refer to the size of the estimate. The relative standard errors table on page 14, provides RSEs for a selection of estimates presented in this publication. It should be noted that estimates for large businesses are generally not subject to sampling error as every effort is made to completely enumerate these businesses.
3 There are about 2 chances in 3 that the difference between the estimate shown and the true value will be within one SE, and about 19 chances in 20 that the difference will be within two SEs. Thus, for example, if the estimated value of a variable is $12,000m and its RSE is 5%, its reliability in terms of sampling error can be interpreted as follows. There are about 2 chances in 3 that the true value of the variable lies within the range $11,400m to $12,600m, and 19 chances in 20 that it lies within the range $10,800m and $13,200m.
4 The size of the RSE may be a misleading indicator of the reliability of some of the estimates for operating profit before tax and industry value added. This situation may occur where an estimate may legitimately include positive and negative values reflecting the financial positions of different businesses. In these cases the aggregate estimate can be small relative to the contribution of individual businesses resulting in an SE which is large relative to the estimate.
5 The imprecision due to sampling variability, which is measured by the SE, is not to 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 collectively referred to as non-sampling error and they may occur in any enumeration, whether it be a full count or a sample.
6 While 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.