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Why overseas merchandise trade data can change

Overseas merchandise trade (OMT) statistics published by Statistics New Zealand are subject to revision and can change after publication. This page explains the reasons why OMT data can change and Statistics New Zealand's processes for revising trade data.

About overseas merchandise trade data

Overseas merchandise trade data provides information on the import and export of merchandise goods between New Zealand and other countries.

How we compile overseas merchandise trade statistics

New Zealand international merchandise trade statistics are compiled in close accordance with the United Nation's International Merchandise Trade Statistics Concepts and Definitions. Any updates and revisions to trade data, and the publication of this data, align with Statistics NZ's principles and protocols for producers of tier 1 statistics.

Why overseas trade data changes

Overseas merchandise trade statistics are published monthly and made available to users as soon as possible, based on a pre-determined monthly release schedule. Statistics are generally released 18 working days after the reference month.

OMT data is published as provisional for the first three months so that late data (ie data received after publication) can be included and updates made as more information becomes available. This process helps to make published trade statistics more accurate. Other revisions may occur occasionally, for example, when confidential data that has been suppressed is made available for publication.

How overseas trade data changes

Data may change due to routine monthly or annual updates, classification changes, or revisions due to errors in the original data.

Monthly updates

Previously published data is revised each month. Late data is included in revised published statistics and amendments are made as more information becomes available. The data we publish remains provisional for the first three months after data is first released. Final figures are published in the fourth month after release. For example, July 2011 data was first published in August 2011 as provisional (version 1); July 2011 data was updated and published in September 2011 (version 2), updated and published again in October 2011 (version 3), with the fourth and final version published in November 2011.

A summary of a 2011 investigation into how overseas merchandise trade data can change after publication can be found on our website.

Seasonally adjusted and trend series

Overseas merchandise trade time series can be split into three components: trend, seasonal, and irregular.

While seasonally adjusted series have had the seasonal component removed, trend series have had both the seasonal and the irregular components removed. Trend estimates reveal the underlying direction of movement in the merchandise trade series, and are likely to indicate turning points more accurately than seasonally adjusted estimates. Overseas merchandise trade trend figures are recalculated each month and the use of new monthly data means that previously published trend estimates are revised. These revisions mainly affect the most recent months. The revisions can be large if a trade value is initially treated as an outlier but is later found to be part of the underlying trend.

Seasonal adjustment removes the estimated impact of regular seasonal events, such as agricultural production cycles, from the merchandise trade time series. This makes the figures for adjacent periods more comparable. Seasonally adjusted figures are estimates and are revised each period, with the largest changes generally occurring in the most recent periods. Seasonally adjusted series are calculated each month and each quarter. Quarterly figures are published in the March, June, September, and December monthly Overseas Merchandise Trade information releases

Annual review of suppressed data

At the request of an exporter or importer, confidential merchandise trade data can be suppressed for up to 24 months. The length of this suppression can be extended further on request. We review data each September and make previously suppressed data available if the suppression is lifted. More information on how overseas merchandise trade confidentiality is applied is available on our website.

Classification changes

Overseas Merchandise Trade data is published according to country groups based on present day membership. Examples of country groupings are the Organisation for Economic Co-operation and Development (OECD), Asia-Pacific Economic Cooperation (APEC), and the Association of Southeast Asian Network (ASEAN). If the members of a group change, the data for that group is revised back to the start of the series.

When other classifications used to publish OMT data change, existing data will not be amended.

For information on other classifications used to publish trade data, see Ways of Looking at New Zealand Merchandise Trade Data.

Revisions due to errors

Revisions due to errors in published data are uncommon. Statistics NZ will consider revising the data only if it results in a substantial change to the chapter-level aggregate data.

Find out about changes to trade data on Infoshare and in our monthly information releases

We publish updates to previous trade statistics in each monthly OMT information release. Individual amendments are not highlighted and are simply incorporated into the next release.

You can find details of when we will conduct the next annual confidentiality review on the Data changes and unscheduled releases page of Infoshare on the Statistics NZ website.

Any revisions due to classification changes or errors in previously published data will usually occur at the same time as the regular monthly release of OMT data. These will be highlighted in the Data quality section of the information release under ‘Period-specific information’.

These revisions will be announced on the Statistics NZ website before the updated release of the OMT data. The information made available will include:

  • the fact the revision is being made
  • the time period for which revisions are being made
  • the commodity codes being revised for each year.

Further information

You can find more information about all the import and export statistics that we produce and overseas merchandise trade monthly releases on our website.

Our release calendar lists all our publications by date of release.

If you require further information, please email

Published: 1 December 2011.  Revised: 23 March 2012 

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