Evidence based policy making is critical for developing sound and relevant government policies. The process of evidence based policy making by definition allows one to monitor specific variables to determine the efficacy of a government intervention. Accurate data and sound data analysis are needed to achieve particular objectives.
In the year of the centenary of the Southern African Customs Union (SACU), the SACU revenue sharing formula is being revised in a manner that is politically sustainable and justifiable to the citizens of SACU. The type and quality of the data used to assess the impact of changes and to guide the choice of alternative formulas will play a critical role.
The objective of this note is to illustrate the existence of large disparities in the trade data. The note also seeks to highlight the extent to which trade datasets are incomplete in the case of SACU countries. More specifically, the focus of this note will be on comparing the SACU trade data available from three sources;
- The TIPS SADC data base was constructed by TIPS through making use of its regional network of in-country government sources attached to various statistical authorities;
- The ITC Trade Map data is based on UN Comtrade with quarterly and monthly data originating from national as well as from regional sources. Data access on the ITC Trade Map is limited to a few years (currently the available trade data series begins in 2001 and progresses to the most recent data available)
- The UN Comtrade database is an internet subscription service that supplies international trade data, as reported by the countries and is maintained by United Nations Commodity Trade Statistics Division. UN COMTRADE does provide free data; although there is a strict limitation to 1 000 records' per day. In both ITC Trade Maps and UN Comtrade, data that is not available from the reporting country is reconstructed on the basis of data reported by partner countries, giving rise to mirror statistics.
- Special attention will also be paid to an additional dataset for South Africa, the Quantec database, because of its popularity amongst South African policy researchers. The Quantec database is an internet subscription service that makes available economic data collections that cover macroeconomic, regional socio-economic, industry and international trade data. It is a database that focuses only on South Africa, and collects data on South African statistics. The trade data is sourced from the South African Revenue Service.
The note contains four main sections:
- The first section gives a brief description of the characteristics of the trade data available for SACU and will focus on the three aforementioned sources.
- The second section will focus on discrepancies in total trade values reported by two databases, between a reporting SACU member and the corresponding SACU partners..
- The third section looks at the statistical significance of the data differences making use of the Wilcoxon Matched-Pairs Signed-Ranks test (Wilcoxon-MPSR test).
- The fourth and final section looks at the results from the statistical analysis