This week sees the release of a number of statistical collections covering sales, which are used to monitor the state of the economy, compile estimates of gross domestic product and its components, and formulate economic policy.
This regular monthly release of data includes wholesale, motor and retail trade sales, and mining and manufacturing production and sales.
May figures for retail trade were released yesterday. They include the resale (sale without transformation) of new and used goods and products to the general public.
A retailer is defined as an enterprise deriving more than 50 percent of its turnover from sales of goods to the general public for household use.
According to the data released yesterday, retail trade sales increased in real terms. At constant (2000) prices for the three months to May, sales increased by 6.9 percent compared with the three months to May 2004.
Retail trade sales at constant prices for January to May increased by 6 percent compared with January to May last year. Retail trade sales at constant prices for May increased 4.8 percent from May 2004.
In terms of the trend cycle for retail trade sales, there was a slight downward trend from January 1998 until mid-2000, followed by an upward trend until the end of last year. A slight decline is reflected this year to date.
How accurate and reliable are these data The answer to this lies in the methodology that underlies the survey. As communicated previously, a steady way of improving the quality of economic statistics is the use of administrative registers?
The monthly survey of the retail trade industry is based on a sample drawn from the Business Sampling Frame that contains businesses registered for VAT and income tax.
Retailers in hardware, paint and glass; and All other retailers, including repair of personal and household goods. Each month, questionnaires are sent to a sample of about 2 500 enterprises from a population of about 46 000 enterprises. Completed questionnaires must be returned to Statistics SA within 10 days after the end of the reference month.
The value of sales is obtained monthly from the sample.
The retail industry is divided into four size groups. All large and medium enterprises (size groups one and two) are completely enumerated. Simple random sampling is applied to size groups three and four (small and very small enterprises).
The total value of sales of size groups one and two is added to the weighted totals of size groups three and four to reflect the total value of sales.
Data gathered from any survey can be subject to both sampling and non-sampling errors. Any information based on a survey is subject to sampling variability: it may differ from the figures that would have been produced if the data had been obtained from all enterprises in the retail industry in South Africa.
The methodologies that underlie the gathering of data on retail trade sales are in line with best statistical practices internationally. The data are also released in conformity with the International Monetary Fund's Special Data Dissemination Standard.
These are important safeguards of data quality, for retail trade sales data, together with other sales data usually released in the same week (wholesale, motor vehicles, mining and manufacturing) provide a vital element in economic monitoring, planning and measuring.
Pali Lehohla is South Africa's statistician-general and head of Statistics South Africa. For more information on Stats SA and its statistical outputs, visit www.statssa.gov.za, or contact user services on (012) 310-8600.