Reported and Converted Data / Conversion...
Reported and Converted Data / Conversion Issues
In general, countries report their detailed merchandise trade data in the latest version of the Harmonized Commodity Description and Coding System (HS). Yet, some countries report their data in earlier HS versions. As a consequence, when querying the data for the latest version of the HS, UN Comtrade is not showing data for all available reporters; and when querying the data for an earlier version of the HS users will obtain data reported in this HS version together with data converted to this HS version.
Converted data are obtained from the reported data by application of the appropriate correlation table [see conversion methodology]. Please note that if the scope of a heading in one classification is split between scopes of several headings in the other classification only an approximate correlation is possible.
Reported classification sometimes is referred also as original classification.
The data conversions have been developed based on the best judgment of the staff at the International Merchandise Trade Statistics Section (IMTSS) of the United Nations Statistics Division (UNSD) but have no binding character whatsoever. Data users are free to convert the original data provided by countries to different classifications according to their own criteria.
Users should understand the limitation of converted data:
Break in time series continuity
HS is amended / revised regularly to add, remove, split or merge commodity codes (Click here for further explanation on how WCO amends / revise the HS). It may cause break in time series analysis for certain commodity code.
Let’s consider this example: 2 older commodity codes merged into 1 commodity code. In this case, data reported in the latest version will be converted to a specific code in earlier version resulting break in series for the other codes. Case study: HS2002 codes 010592 and 010593 are merged into HS2007 code 010594. Based on the conversion table, HS2007 code 010594 is converted to HS2002 010592 resulting break in series for HS2002 code 010593.
Loss of confidential information
Some countries suppress confidential data in 4 and 6 digit level and reveal them on 2 digit level. In reported data, 2 digit level contains, in addition, also the confidential data (therefore sum of 2 digits is greater than sum of 6 digits). In the contrary, in converted data, 2 digits does not contain confidential, because HS conversion is done on the most detailed level (therefore sum of 2 digits is equal to sum of 6 digits).
Possible loss of supplementary quantity information
Supplementary quantity is converted along with trade values. For those with split correlations (single old codes split into several new codes), values can be aggregated straightforward however net weight and supplementary quantity may not be able to be aggregated because in multiple reported quantity units in reported classification.
Data Extraction Option
Because of those issues, for some users, it may be more useful to extract data in reported classification across many reporters and years. Before March 2009, UN Comtrade did not offer that option, users must select one version of the classification then extract the data in that classification. Now, in addition to data extraction in different commodity classifications, it is possible for user to extract at once data for all reporters in the original classification in which it was reported. In both, Basic and Express Selection, users can select HS “as reported” or SITC “as reported” to extract data in the original classification (essentially all countries report now in the HS but in earlier years SITC was used). For additional metadata, such as version of the original classification or original currency, please consult the Explanatory Notes or Data Availability by Date of Loading.
Note of caution: users should understand some codes changed in scope from one version to another. By combining them, in one data extraction, may result break in time series analysis.
In some data availability pages, reported and converted classifications are colored coded. Classifications appearing in GRAY represent data reported by country. Classifications appearing in BLUE/RED represent converted data.
Useful related Links:
- Complete HS and SITC conversion and correspondence tables along with detailed note on its conversion methodology;
- UN Comtrade Explanatory Notes;
- UN Comtrade Data Availability by Date of Loading.
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Last Modified:Tuesday, January 19, 2010
Last Modified By: comtrade_admin
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