The Australian Bureau of Statistics ( ABS ) has announced
revisions to the Retail Business Survey (RBS), which provides the
information for its regular Retail Trade publication. This feature
discusses the changes and the implications for the Monthly
statistical bulletin.
What is
changing?
The RBS is used to estimate the value
of the turnover of retail businesses in Australia. The ABS reports
that three changes will be made to the RBS. These changes include
removing some sectors from the survey, reducing the survey sample
size and changing the sampling method.
The RBS will no longer include the
hotels and licensed clubs sector and the selected services
industries sector. These exclusions reduce the size of the
‘completely enumerated’ sector from 730 to 640
businesses, and sampled businesses from 3214 to 2775—a
reduction of 13 per cent in businesses surveyed. (The
enumerated sector includes major retailers such as department
stores, and the sampled sector includes all other retail
businesses).
The survey size will also be reduced
for the businesses that remain in the survey. The completed
enumerated sector size will fall from 640 to 500 businesses, due to
a reclassification of businesses through size. For the
sampled sector the survey sample will be reduced from 2775 to 2702
businesses. The combined reduction in survey sample size will
be around six per cent.
The monthly activity is also affected
by the change in sampling methodology, not just the sample
reduction. Typically, the RBS would survey businesses on a monthly
basis. That is, before the change, 3944 businesses would have been
surveyed each month. After the change, the survey will be run
monthly; however, the survey will include only 1401 businesses.
This figure includes the completely enumerated sector’s 500
businesses, each month, and only 901 sample sector businesses. For
the latter sector, the monthly target is derived from sampling 901
businesses per month, over a three month period, so that 2702
businesses are sampled per quarter.
Why does it
matter?
A survey measures responses to
questions from a sample of participants within a population. The
intention is to estimate statistics from the sample, such as
average monthly turnover, which can be used to estimate, or infer,
the approximate values of a population as a whole.
Surveys contain sampling errors which
occur because they do not cover an entire population, as in a
census. While understanding the cause of, and reasons for, the
errors is not critical it is important to understand that as the
sample size decreases, the errors from the sampling exercise
increase. Therefore, reducing the scope and sample of the RBS
mean the retail trade data are less accurate.
The ABS provides details of the RBS
sampling error by publishing the relative standard errors ( RSE )
for the retail trade data. According to ABS’ estimates,
the reduced sample size will cause an increase in the monthly RSEs
of between 30 per cent and 100 per cent, depending on the
sector or State being considered.
What will be
available?
As a consequence of the discussed
changes the retail trade information will be split into two
components. The first component will be a monthly report
‘Retail Trade Trends’. This report will provide trend
estimates of broad industry groups and State totals, but limited
industry level details. Additional information will be provided,
such as seasonally adjusted data, but is considered too volatile
due to the smaller sample size and associated higher RSEs.
The second component will be a
quarterly publication ‘Retail Trade Quarterly
Indicators’. This publication will be more reliable than the
monthly report. It will include original, seasonally adjusted and
trend details for industry and sub-industry data, at the Australian
and State levels. The publication will also include chain volume
estimates to provide inflation adjusted turnover.
What is the expected impact
on the data?
The immediate impact of the changes
will be to lower the value of sales activity reported, compared to
the previous series. The impact of the sample size and
methodological change will be to reduce the reliability of retail
trade data.
The ABS has estimated that the
revisions would have seen a 0.3 per cent smaller measure of retail
trade for June 2008 data. To see how the series compare over time,
the graph below shows the pre and post change seasonally adjusted
series from April 1982 (based on ABS backcasts) to June 2008. It is
clear that total retail trade is now lower.
Monthly trade data under different methods
Monthly statistical bulletin
Table 4.1
Monthly statistical bulletin Table
4.1 reports seasonally adjusted monthly retail sales data. As a
consequence of the changes, the monthly data will be replaced by
quarterly seasonally adjusted retail sales data, once the quarterly
series begins being published in November 2008. When the
quarterly ABS report is published, this bulletin will incorporate
all backcast data for consistency, and any further changes will be
advised.
Adrian
Makeham-Kirchner
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