6248.0.55.001 - Wage and Salary Earners, Public Sector, Australia, Jun 2004
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 23/09/2004
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TECHNICAL NOTE - DATA QUALITY

RELIABILITY OF ESTIMATES

1 As the estimates from the Survey of Employment and Earnings are based on information collected from a sample of public sector employers rather than a full enumeration, they are subject to sampling variability. That is, they may differ from the estimates that would have been produced if the information had been obtained from all public sector employers. This difference, called sampling error, should not be confused with inaccuracy that may occur because of imperfections in reporting by respondents or in processing by the ABS. Such inaccuracy is referred to as non-sampling error and may occur in any enumeration whether it be a full count or a sample. Efforts have been made to reduce non-sampling error by careful design of questionnaires, detailed checking of returns and quality control of processing.

2 The sampling error associated with any estimate can be estimated from the sample results. One measure of sampling error is given by the standard error which indicates the degree to which an estimate may vary from the value that would have been obtained from a full enumeration (the ‘true value’ ). There are about two chances in three that a sample estimate differs from the true value by less than one standard error, and about nineteen chances in twenty that the difference will be less than two standard errors.

3 An example of the use of standard error on levels estimates is as follows. If the estimated number of employees was 1,400,000 with a standard error of 3,000, then there would be about two chances in three that a full enumeration would have given a figure in the range 1,397,000 to 1,403,000 and about nineteen chances in twenty that it would be in the range 1,394,000 to 1,406,000.

4 An example of the use of standard error on movements is as follows. If the estimated standard error for a quarterly change estimate of employees was 2,000 and the quarterly change estimate between two quarters was 10,000 persons, then there would be about two chances in three that a full enumeration would have given a quarterly change estimate in the range 8,000 to 12,000 persons and about nineteen chances in twenty that it would been in the range 6,000 to 14,000 persons.

5 Quarterly movements in estimates of employees and earnings are considered to be statistically significant where they exceed two standard errors.

6 Another measure of the sampling error (for level estimates only) is the relative standard error, which is obtained by expressing the standard error as a percentage of the estimate to which it refers. Estimates with relative standard errors greater than 25% are not considered sufficiently reliable for most purposes and should be used with caution.

7 The following table shows the standard errors for level and movement estimates based upon data for the current quarter. Standard errors for other estimates are available on request.

 STANDARD ERRORS, Public sector employees and gross earnings May 2004 June Quarter 2004 Employees ('000) Gross Earnings (\$m) C'wealth State Local Total C'wealth State Local Total LEVEL New South Wales 0.5 0.6 1.4 1.4 7.8 8.7 14.0 14.8 Victoria 0.9 1.9 1.2 1.9 14.5 15.4 8.8 17.5 Queensland 0.7 1.9 1.0 2.1 9.6 18.7 8.8 20.7 South Australia 0.3 0.6 0.6 0.4 4.5 7.7 6.5 4.5 Western Australia 0.9 0.8 1.2 1.1 12.2 8.3 11.9 11.5 Tasmania 0.2 0.2 0.2 0.2 2.3 1.3 1.5 2.2 Northern Territory 0.1 0.3 0.1 0.3 0.9 0.6 0.5 0.9 Australian Capital Territory 0.4 0.1 na 0.4 6.8 1.3 na 6.5 Australia 1.6 3.0 2.5 3.4 24.2 28.2 23.2 34.0 QUARTERLY MOVEMENT New South Wales 0.9 0.8 0.8 0.8 10.6 12.5 8.7 11.6 Victoria 0.6 2.3 0.5 2.3 5.7 14.8 3.7 15.0 Queensland 0.5 0.9 0.9 1.3 7.2 10.2 9.3 14.5 South Australia 0.1 0.2 0.1 0.2 1.7 2.6 1.8 2.8 Western Australia 0.4 0.6 0.8 0.9 6.2 6.5 8.7 9.4 Tasmania 0.1 0.1 0.1 0.2 2.5 0.8 0.6 2.4 Northern Territory - 0.2 0.2 0.2 0.7 0.3 1.2 1.2 Australian Capital Territory 0.6 0.3 na 0.5 10.0 3.5 na 9.3 Australia 1.4 2.7 1.5 3.0 18.6 23.3 16.0 27.5 - nil or rounded to zero (including null cells) na not available