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11. However, for a minority of businesses the correlation between reported data and annualised BAS Turnover is not as strong. There are two main reasons for this. First, all units selected in the Retail Business survey have their industry classification checked and some are identified as being predominantly non-retail. Second, some businesses selected in the survey are discovered to have ceased trading or are seasonal operators. These non-retail and non-operating businesses contribute nil to the Retail Trade estimates even though they have an annualised BAS Turnover value.
12. To further improve the efficiency of the estimation, businesses selected in the Retail Business survey will be post-stratified prior to estimation into those with reported data and those with nil data. Graph 3 illustrates the improved correlation when adjustments have been made for the issues discussed above. The key feature of the chart below in comparison to graph 2 is the removal of a number of units that have a high annualised BAS Turnover value and a zero Retail Trade estimate.
13. For the Retail Business survey, the generalised regression estimation model has been fitted at the state and publication industry level. This is the broadest level at which the model can be fitted to control estimates at the state and industry levels; it is also the most robust.
14. The ABS is currently exploring the possibility of introducing the generalised regression estimation methodology into other business surveys. Initial work indicates that the Quarterly Business Indicators survey is likely to benefit from this methodology. Users will be advised of this work in relevant publications.
15. The current Retail Business survey sample design was last determined in 1994, with the allocation using employment as a sizing variable. Originally, this design was determined to meet target relative standard errors (RSEs) at the state, publication industry and Australian levels, using ratio estimation with employment as the estimation benchmark. The design had some minor adjustments in 2002 to account for the statistical infrastructure associated with the introduction of TNTS including the current modelled employment size measure replacing employment as a stratification variable. Currently, the target RSEs for all the publication industries and the smaller states are met but some inefficiencies have crept into the application of the design.
16. New stratum boundaries based on annualised BAS Turnover have been determined which keep the completely enumerated sector (predominantly large or complex businesses) at a size similar to the current design. The completely enumerated sector contributes about 55% of the total estimate. This ensures a reliable total estimate. Additionally, production of state estimates are heavily dependent on survey responses from the completely enumerated sector. As such, any significant reduction in the coverage of these businesses would be problematic for the quality of the total estimates and the finer dissections. Consequently, most of the reductions in the number of respondents to the collection are in the sample sector.
17. The new sample design will result in RSEs that are, on average, close to the design RSEs and similar to the RSEs currently achieved for level estimates. RSEs for movement estimates should be improved.
18. As a consequence of the new design and the new estimation methodology, the sample size of the Retail Business survey will be reduced from about 5,300 businesses to about 4,350 businesses. The new sample of 4,350 businesses will include about 2,200 businesses newly selected in the Retail Business survey. This once-off high proportion of newly selected businesses compares to the 400 to 500 businesses that are normally newly selected in the collection each quarter. Subsequent to the introduction of the new sample design, the number of newly selected businesses each quarter is expected to be less than was the case with the previous design.
Impact on the time series
19. The changes to statistical infrastructure introduced in July 2002 had a significant impact on the Retail Trade series and this was managed by measuring the impact and revising the historical series to make them as continuous as possible.
20. The changes currently being introduced should not have as significant an impact on the Retail Trade series because the statistical units and the population will not be changing as occurred in July 2002. However, the introduction of revised stratification, the use of a different estimation methodology and the impact of a large number of new businesses being included in the sample may result in a once-off change to the level of the series. The level of change in individual Retail Trade series will vary.
21. For the June 2004 reference month both the old and the new sample designs will be used for the Retail Business survey (a parallel run), to determine any observed difference between the estimates compiled on the new and old basis. Estimates from the old sample design will be used in the June 2004 reference month issue of this publication. In the July 2004 reference month of this publication, the results from the new sample design will be used for both July 2004 and June 2004 estimates (i.e. movement estimates for July will be based on the new sample design). Estimates for historical periods will be revised by smoothing in the difference between the estimates from the old and new samples back to 1982. This will preserve the movement estimates.
Change to industry detail
22. Another change that will be occurring in the July reference month as a result of the new sample design is the combination of 'Toy and game retailing' and 'Sport, camping equipment and photographic equipment retailing' into a single industry for stratification purposes. These industries were previously stratified and seasonally adjusted separately and then combined onto 'Other recreational goods retailing' for publication. While this change has no impact on the range of data available in the publication, data for these two industries which were previously released separately as part of the special data service for Australia only (data at the state level were confidential), will no longer be separately available.
Impact on the national accounts
23. As historic Retail Trade estimates will change due to the smoothing process described above, there will be an impact on the quarterly chain volume measures, as well as the final household consumption expenditure component of GDP. The chain volume measures on the new basis will be released with the August 2004 issue of this publication, and the national accounts estimates on the new basis in the September quarter 2004 Australian National Accounts: National Income, Expenditure and Product (cat. no. 5206.0). The smoothing exercise should mean that historical movement estimates will be little changed.
24. The seasonal and trading day factors used in the Retail Trade series are reviewed annually at a more detailed level than possible in the monthly processing cycle. As concurrent seasonal adjustment is used, this annual reanalysis does not normally result in significant changes. For Retail Trade, the results of the latest review are usually shown in the July issue each year. Given that the difference between the new and old estimates will be backcast through the historical estimates, the annual seasonal reanalysis will be delayed a month and the results included in the August 2004 issue.
25. The ABS is also currently investigating the feasibility of using improved methods to calculate seasonal factors. These investigations are focused on the potential application of ARIMA modelling techniques. The expectation is that these techniques will reduce revisions in the seasonally adjusted estimates at the current end of the series by the magnitude of six to seven percent. The magnitude of the revision may be different for individual series. It is expected that ARIMA modelling will be first introduced for the Retail Trade series, along with the annual seasonal reanalysis in the August 2004 issue. More detail on the use of ARIMA modelling for seasonal adjustment purposes can be supplied on request.
26. Further details on the impact of introducing the new sample design and estimation methodology will be included in the July 2004 issue. If you have any queries before then, please contact Michael Gurney on 02 6252 5487 or email firstname.lastname@example.org.
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