Yesterday, Statistics SA released the latest information for motor, retail and wholesale trade sales.
Retail trade sales increased by 10.
Motor trade sales increased by 17.
Wholesale trade sales increased by 13.6 percent.
Economists watch these results carefully as they provide important performance and trend indicators for the economy as a whole.
Data from these trade sales surveys are used to compile estimates of the gross domestic product and its components, which are used in monitoring the state of the economy and in the formulation of economic policy.
Each of the three areas is surveyed monthly. For the motor trade, the enterprises surveyed include motor vehicle dealers, filling stations and workshops; motor cycle dealers; spares and accessories; tyre dealers; automotive electricians; radiator repairs; panel beaters and spray painters; other specialised motor repair services; and other motor trade.
The survey is conducted by mail, and questionnaires are sent to a sample of about 600 enterprises from a population of about 11 000 enterprises.
The motor industry is divided into four size groups.
Size group one, which comprises about 50 percent of the enterprises in the current sample, is completely enumerated.
Simple random sampling is applied to group two (medium-sized) enterprises, and to size groups three and four (small) enterprises.
The total value of sales of the large enterprises (size group one) in a division is added to the weighted totals of size groups two, three and four to reflect the total value of sales.
The wholesale trade includes the resale (sale without transformation) of new and used goods and products to other wholesalers, retailers, and agricultural, industrial, commercial, institutional and professional users either directly or through agents on a fee or contract basis.
This survey covers wholesale trade on a fee or contract basis; foodstuffs, beverages and tobacco; livestock and farm products; textiles, clothing and footwear; furniture and household requisites; office and shop equipment, books and stationery; diamonds, jewellery and silverware; pharmaceutical and chemical products; construction and building materials; machinery and equipment; and miscellaneous.
Questionnaires are sent to a sample of about 800 from a population of about 19 000 enterprises. The wholesale industry is divided into four size groups.
All large enterprises (size group one), which comprise about 60 percent of the enterprises in the current sample, are completely enumerated.
Simple random sampling is applied to groups two (medium-sized) enterprises, three and four (small). The total value of sales of the large enterprises (size group one) is added to the weighted totals of size groups two, three and four to reflect the total value of sales.
The monthly retail trade survey covers butchers; general dealers; bottle stores; dealers in clothing, footwear and textiles; dealers in furniture and household requisites; bookstores and stationers; jewellers; chemists; dealers in miscellaneous goods; and repair of personal and household goods.
Questionnaires are sent to a sample of about 3 000 from a population of about 28 000 enterprises.
The retail industry is also divided into four size groups. All large enterprises (size group one), which comprise about 11 percent of the enterprises in the current sample, are completely enumerated.
Simple random sampling is applied to size groups two (medium-sized), three and four (small) enterprises.
The total value of sales of the large enterprises (size group one) is added to the weighted totals of size groups two, three and four to reflect the total value of sales.
How accurate are the data presented All sample surveys are subject to sampling variability. This means that data presented might differ from the figures that would have been produced if the data had been obtained from all enterprises in the relevant industries. Estimates are therefore subject to sampling errors?
Inaccuracies may also occur because of imperfections in reporting by enterprises and errors made in the collection and processing of the data. Inaccuracies of this kind are referred to as non-sampling errors.
Every effort is made to minimise non-sampling errors by careful design of questionnaires, testing them in pilot studies, editing reported data and implementing efficient operating procedures.
Figures released for the latest month (December 2004 in this case) are preliminary, and fluctuations may occur in consecutive months as a result of seasonal and economic factors.
Pali Lehohla is South Africa's statistician-general and head of Statistics SA. For more information on Stats SA and its statistical outputs, including yesterday's releases on retail, wholesale and motor trade sales, visit www.statssa.gov.za, or contact user services on (012) 310-8600.