This page outlines how we apply confidentiality to overseas trade data.
Applying confidentiality for overseas trade data differs from the process we use for all other Statistics New Zealand outputs. This can cause some confusion to users. Consequently, we are providing a practical, step-by-step example of how confidentiality is applied.
This example is based around the fictional company Sporting Goods Ltd, which exports rugby balls (which have the 10-digit Harmonised System (HS) code 9506.62.00.21: Balls, inflatable for rugby union and rugby league) all around the world.
Sporting Goods Ltd has decided that, due to tight international competition, they would like to suppress how many rugby balls they exported, how much they sold them for, and where they sold them.
How to apply for confidentiality
Sporting Goods Ltd writes us a letter, which includes the following information:
- the New Zealand Customs Service client code(s) they use to export or import
- the 10-digit New Zealand Harmonised System classification/tariff code they want suppression for
- the activity they are involved in (importing or exporting)
- how long they want suppression for
- the reason they want to suppress the data.
For more information on this part of the process, please see the international merchandise trade statistics confidentiality policy.
Once we receive this letter, we carry out tests on the rugby ball code (9506.62.00.21). These tests check whether Sporting Goods Ltd's data is identifiable. If the tests confirm the data showing the export of rugby balls does make the company’s data identifiable, this code is suppressed.
Suppression period options available
Sporting Goods Ltd needed to select how long a period they want their data suppressed for. The company had three options available:
- A rolling three-month period
Every month, we release four months of overseas trade data – the latest month, plus a re-release of the previous three months. For a three-month request, the relevant HS code(s) will be suppressed for the latest month, and the previous two months. On the fourth month, we lift the suppression and data for the suppressed values will be visible again.
In September each year we update the periods for which the 12-month suppressions are active. After this is done, only the latest trade year (the year ended June) and the months since then, are suppressed. For example, in September 2010, suppression of codes in the 12 months between July 2008 and June 2009 was reversed. This means previously suppressed data was then available for users. However, data for these suppressed codes that is produced after July 2009 is suppressed until September 2011, when the process starts again.
The process for the 24- month period is basically the same as for the 12-month period, but with a few small differences. Instead of only the latest trade year and the months since then being suppressed, we suppress the latest two trade years and the months since then. In certain circumstances this may extend to three or more trade years being suppressed.
How we apply confidentiality to the data
We apply suppression in the overseas trade data by changing the HS code. Using the example above, rugby balls (9506.62.00.21) would change to the confidential items code (9809.00.00.00). We do this for all destination countries, and for all exporters using this code – not just the values that Sporting Goods Ltd has exported, or just the countries that Sporting Goods Ltd exports to.
Because we change to the confidential items code for every suppression, the HS code 9809.00.00.00 becomes a pool of suppressed codes, hiding each other’s values. We combine the total of HS code 9809.00.00.00 with all other HS codes to calculate the correct total of exports.
Ten-digit HS codes can be aggregated together to create six-digit HS codes. These six-digit HS codes aggregate to four-digit codes, which in turn, aggregate to two-digit codes. The downside to the way we suppress overseas trade data is that the HS aggregations (two-digit, four-digit, and six-digit levels) will not include the value of the suppressed 10-digit code.
In the Sporting Goods Ltd example, the 10-digit value for rugby balls is suppressed. The value of the related six-digit HS code (9506.62: Balls, inflatable) includes basketballs and netballs, but not the value of rugby balls. The value of rugby balls is now reported in the confidential HS code, and as a result, the total exports value is not affected. The table below shows the effect of suppression on the value of exports:
|Example showing the effect of confidentiality on exports
||Value before suppression ($)
||Value after suppression ($)|
|95 (2-digit level)
||Toys, games, and sport equipment
||NZ misc provisions
|Symbol: .. figure not available
Published 16 September 2011