The nature of statistical revision and change, which is a hallmark of continuous processes of quality improvement, has often been discussed in Inside Statistics.
Attention has also been drawn to the necessary balancing of stability and change. Continuity in time-series is essential so that long-term comparisons can be made and improvements in quality based on new methodologies and better coverage of the economy can introduce discontinuities in long-range comparability.
National accounts are influenced by improved quality and more extensive coverage of economic activity.
For example, gross domestic product (GDP), which is an output of national accounts, is based on a range of statistical data sources that are consolidated into a single coherent system. Changes in these data sources, whether as a result of revision to data or the methodologies used to gather the data, naturally influence the calculation of GDP.
Revision of previous GDP estimates and rebasing and benchmarking have also been discussed and explained. Although the effect of these factors will be seen most clearly in November, when GDP data will be released, revision of estimates is a routine part of national accounting.
The international standard South Africa adheres to (the UN system of national accounts) requires national accounts estimates to be benchmarked frequently. Statistics SA aims to do this at least every five years.
Stats SA is not alone in its concerns that some roleplayers do not seem to have understood the routine nature of statistical revision.
Len Cook, the head of the UK's Office of National Statistics (ONS), noted in a recent paper that "revisions to key economic series produced by ONS [have] attracted a great deal of comment and criticism. However, this reaction has not always acknowledged the complex statistical framework within which revisions take place. Revisions to official statistics are expected and inevitable."
In his paper, Cook referred to a Swedish report comparing GDP revisions made in 11 countries over nearly 20 years - a powerful indication of the routine nature of statistical revision, particularly in national accounts. Cook argued that absolute stability and continuity in statistical series in a fast-changing world were "naive" expectations on the part of users.
"We have seen rapid change in the target populations of nearly all statistical sources, whether they relate to persons, businesses, products, transactions or life events. Our statistical tools are also changing rapidly, bringing new expectations of what they should deliver."
It is of concern that the routine nature of statistical revision has been misunderstood by some commentators. Worse is the attribution of a conspiracy to this transparent and routine activity.
To suggest that "South Africa's GDP is about to change in strange ways when figures are released in November" because "Stats SA is altering the way the GDP figure is calculated" - as a columnist in a Sunday newspaper recently did - is to seek conspiracy in what is both ordinary and transparent.
Perhaps the final word is best left to Cook, one of the best respected and most experienced of national statisticians. Calculation of economic measures, he noted, "relies upon assumptions of continuity for structures and structural relationships for fixed periods. From time to time the underlying structural assumptions are updated giving rise to potential revisions."
Pali Lehohla is South Africa's statistician-general and head of Statistics SA. For more information on Stats SA and its outputs, visit www.statssa.gov.za or contact (012) 310-8600.