Gross domestic product (GDP) estimates compiled from both the production and income approaches rely on a variety of economic and social data sources. These data sets cover economic activities in the various industries (agriculture, mining, manufacturing, trade and so on) of the economy.
Over the past few years, Statistics SA has engaged in a continuous improvement strategy for its economics statistics. This has involved an improvement in the quality of basic economics statistics as well as the GDP estimates derived from these statistics.
The benchmarked and rebased GDP estimates that were published at the end of November 2004 were an output of this strategy. Economic activity is measured through surveys that differ in frequency.
Short-term surveys entail monthly and quarterly data collection, while long-term measurement is undertaken bi-annually, annually or sometimes even less frequently.
The annual economic activity survey (EAS) is one of the most important long-term tools used for the estimation of annual GDP. In addition to the EAS, the improvement strategy also makes provision for in-depth coverage of the total economy over a three-year period through an instrument referred to as a large sample survey (LSS).
More detailed than the EAS, the LSS is the data set from which the cost structures of the various economic industries are sourced.
While data sets such as the LSS and EAS form the basis of the components of the annual GDP estimates, short-term samples such as the quarterly employment survey (QES) are used as an indicator for a specific variable, for example, compensation of employees.
Through the QES, the quarterly trends are established until the next annual estimate of the same variable is available through an annual data set (EAS and/or LSS). National accounts estimates rely on a combination of short- and long-term surveys.
Not only are different data sets used for the compilation of GDP estimates, but these data sets are also assembled through different collection methods. Most economic data sets are collated through postal surveys, where a questionnaire is mailed to the respondent, who completes it and then returns the document via a business reply envelope.
In a second collection method, direct price collections, an enumerator visits a retail outlet and collects the prices of the required products. Other data is sourced from administrative records, including year books, annual reports or government records such as, for example, the number of building plans passed and completed.
Data that feed into GDP estimates are also collected through household surveys such as the income and expenditure survey, and the labour force survey. These are conducted by field staff employed and trained by Stats SA.
GDP estimates are compiled through an input-output framework, as this allows for the comparison and confrontation of all data sets in a comprehensive and systematic manner. It also combines the three different approaches (production, income and expenditure) for GDP compilation. This is why the use and analysis of a single data set cannot provide a solid basis for criticism of the complex and multisourced estimation of GDP.
Comparison and confrontation of new data, as well as routine revisions to economic data sets (both short- and long-term) will culminate in the publication of the latest GDP estimates on November 29. This will include revised annual and regional estimates for 2002 to 2004 as well as quarterly estimates up to the third quarter of 2005.