Quality Assurance

Quality assurance of collected data is a significant part of the compilation process prior to publication of the OTS. Post-publication quality assurance is also conducted where potential anomalies are identified. The following content provides information detailing: how data users can assess the quality of published data, how to challenge the published data, and access to outcome reports from past quality assurance activity.  

Overview PowerPoint of how the OTS meets key quality requirements

A summary overview of how the overseas trade statistics (OTS) meets key quality requirements. Available to download here: OTS Quality Overview (pps)

Quality Standards 

In order to enable users to judge whether data outputs meet their needs, it is recommended that output providers report quality in terms of the six output quality dimensions of the European Statistical System (ESS) which are defined in EU legislation.
For international trade statistics these are further divided into more specific indicators of quality as detailed in the Eurostat (EU Statistical Office) DOC MET 1000 requirements. The quality of the OTS are judged against these indicators, in line with EU legislation.
The UK Government Statistical Service (GSS) also publish guidelines that contain a wide range of quality measures and indicators, grouped together using the six ESS output quality dimensions. Some of these indicators are also used in the OTS quality reporting. 

Information on OTS Quality

EU Member States are required by legislation (see Related Links) to collect data on international trade. The implementing regulations specify that Eurostat will carry out an annual quality assessment based on quality indicators and requirements agreed beforehand with the national authorities.’
 The quality indicators are those specified in the DOC MET 1000 document mentioned above. Here is the latest Eurostat assessment of the UK international trade data.
Eurostat also produce a Summary Quality Report for all EU Member States, and an annual EU Quality Report.
In addition to their assessment of the data, Eurostat also have a rolling programme of visits to Member States to discuss data production methodologies. Here is the final report on the most recent visit to the UK. 

Statement of adherence to EU legislation 

The latest summary of how the OTS complies with EU legislation governing its methodology is now available. 

Balance of Payments 

OTS data also contribute to the Balance of Payments publication produced by the Office for National Statistics (ONS). ONS have a quality requirement that 92% or more of the value of the first detailed EU trade output, should have come from business declarations. The remainder of the data provided is estimated. An assessment of this quality criterion is shown in the graph.   

Quality Report

HMRC Trade Statistics also produce a regular OTS & RTS Quality Report based on the GSS guidelines referred to above. Here is the latest report

Trade challenge

Data users who believe the detailed, published trade data to be incorrect may contact HMRC Trade Statistics to challenge the data quality. To do so, the user should email Customer Services, providing details of: the period, flow (import, export, arrival, dispatch), the full detail of the line of trade, the specific field value being queried (with potential alternative if known), and stating why they consider it to be incorrect. The challenge will be acknowledged, allocated a reference number and investigated subject to resource availability. This may take a considerable period of time as documentary evidence such as copy invoices may be required from all businesses involved in the trade.
If the published data are found to be incorrect, a revision will be made in accordance with the OTS Policy on Revisions (see 'Policies and Methodology'). The user making the challenge will not be provided with specific details of the revision to be made, as the revised data will be released to all users concurrently via this website, in accordance with the Code of Practice for Official Statistics.


Asymmetries are the differences between the trade statistics of partner countries. As each country collects data on their own international trade-in-goods for both imports and exports, the 'mirror flow' (country A's exports to country B, and country B's imports from country A) should in theory match. In practice, the figures do not match and an 'asymmetry' for the period in question can be measured.
Here is a detailed overview of asymmetries.
Reports explaining the asymmetries the UK shares with the rest of the EU, and the reasons for these are available here:
Date Published Report
April 2013​ A Reconciliation of Asymmetries in Trade-in-Goods Statistics Published by the UK and Other European Union Member States - April 2013
July 2012 A Reconciliation of Asymmetries in Trade-in-Goods Statistics Published by the UK and Other European Union Member States
October 2011

A Reconciliation of Differences in Trade-in-Goods Statistics Published by the UK and Other European Union Member States – October 2011

June 2009
November 2008
March 2008
EDICOM Report 53102.2007.001-2007.449. - Bilateral analysis of asymmetries between Ireland and the UK.
December 2005
EDICOM Report 200453202016 (pdf) - Bilateral analysis of asymmetries in foreign Trade Statistics between Germany and the UK.
December 2005
EDICOM-Report 200453202017 (pdf)  - Analysis of asymmetries in intra-EU trade statistics with particular regard to the impact of the Rotterdam and Antwerp effects.