Initial draft as of May 2008
Quantity and Weight information in UN Comtrade
Introduction of a new system
A new system of providing information on supplementary quantity and net weight has been
introduced starting 1.1.2006 with the implementation of a new processing system. This new
system has three core elements:
1. Quantity and weight information are accommodated in two separate data fields which allows
to have information on the supplementary quantity and net weight at the same time. This is in
line with the international recommendation to compile the supplementary quantity and in
addition net weight where appropriate (IMTS, Rev.2, para. 133).
2. For the supplementary quantity the recommended quantity units of the World Customs
Organization (WCO RU) are enforced in order to allow comparability across countries. This
means that the quantity information reported for a particular commodity has to be reported in a
WCO RU or it must be possible to convert it into a WCO RU. Otherwise the quantity
information is disregarded.
3. Any missing quantity or net weight information and disregarded quantity information is
estimated (to the extend that such an estimation is possible). In addition, for a limited number of
records per country extreme values for quantity and net weight are replaced with estimated
values (see Annex 1 for details).
The previous processing system was able to accommodate only either net weight or
supplementary quantity in case both were provided. Also there was no procedure to ensure that
the quantity information for individual commodities would follow a specific quantity unit.
The new system came into force 1.1.2006 and all data with the reporting year 2005 and later has
been processed using this new system. Yet, UNSD is also reprocessing data back to the year
2000 with the goal to provide all data starting with the reporting year 2000 according to this new
processing standard.
Best possible use of information provided
Estimation of quantity and net weight are only the last resort. The following steps are undertaken
to make the best possible use of the information provided by the country:
a) Net weight is copied into the supplementary unit and vice versa in all cases where only
one of them is reported.
b) During code normalization conversion factors are used to convert supplementary
quantities reported in non-standard quantity units into quantities of WCO standard units.
Such conversion factors can be mathematical or empirical. Countries are requested to
establish and provide a comprehensive list of such conversion factors.
c) There is also an automatic conversion using conversion factors provided by FAO.
d) In addition, there is also a automatic conversion of Number(5) to/from Thousands (9);
Number(5) to/from Dozen (11); Kg (8) to/from Carat and Liter (7) to/from meter cubic
(12)
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Initial draft as of May 2008
Estimation methodology
Estimation of quantity and net weight is performed in three cases: a) Data has not been provided;
b) Provided data is disregarded as it does not conform with and cannot be converted into WCO
RU and c) Quantity or net weight provided is extreme. There are two estimation procedures:
1. Using partly reported quantity and/or net weight in the same commodity/unit/flow
(Weighted Unit Value):
In order to use the partly reported quantity and/or net weight to be used to estimate non-reported
quantity and/or net weight, it has to pass the confidence threshold. For OECD countries, the trade
value share of partly reported quantity and/or net weight must be more than 20%, and for nonOECD countries must be more than 50%.
2. Using Standard Unit Value (SUV)
Standard Unit Value (SUV) is used to estimate net weight and quantity whenever Weighted Unit
Value is not available. SUV was calculated at the end of the year and are used for quantity and/or
net weight estimation or outliers detection. Please refer to SUV methodology for detailed
information.
Documentation of estimations
1. Estimation Flag available on UN Comtrade
Estimated records are clearly identified by an estimation flag and are shown in italics (at result
page). By default, the estimation flag is part of download format.
The estimation flag possible values are:
0 = no estimation
2 = quantity estimation only
4 = netweight estimation only
6 = both quantity and netweight are estimated.
2. Footnotes are generated describing the estimation procedure used.
The footnotes can be downloaded separately from the data records. Please note that one record
can have more than one footnote. The following footnotes are provided:
In case of missing net weight quantity
1) Net weight estimated using Standard Unit Value
2) Net weight estimated using Weighted Unit Value
3) Supp Qty estimated using Standard Unit Value
4) Supp Qty estimated using Weighted Unit Value
In case of extreme quantity and net weight
5) SUV applied for weight. Original UV: [ ]
6) SUV applied. Original UV: [ ]
In addition:
7) Supp Qty Unit set to ‘No Quantity’ because SUV is not available
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Initial draft as of May 2008
Annex I: Extremes Unit Values Criteria
For both quantity unit and net weight and partner World, there are three checks:
1. Historical Unit Value Check
Unit Values are considered extreme if ():
- Value is more than 0.005% of Totals
- Unit Value is more than maximum of historical unit value * 10
- Unit Value is less than minimum of historical unit value / 10
2. Standard Unit Value Check
Unit Values are considered extreme if ():
- Value is more than $50,000
- Unit Value is more than upper limit of standard unit value * 2
- Unit Value is more than upper limit of standard unit value / 2
3. Historical Value Check
Values are considered extreme if:
- Value is more than $1,000,000
- Value is more than maximum of historical value * 100
- Value is less than minimum of historical value / 100
Not all extremes unit values are corrected, only 5% of them (because the checks are done only
with partner world, the 5% only applies to combination of commodity – trade flow).
Then the ratios of unit values are calculated to determine the sorting order:
If unit value < minimum unit value then ratio = minimum unit value / unit value
Otherwise ratio = unit value / maximum of unit value
The top 5% ratios will be corrected by applying standard unit value for all partners.
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