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Overseas Merchandise Trade: January 2012
Embargoed until 10:45am  –  27 February 2012
Data quality

Period-specific information
This section contains data information that has changed since the last release.

General information
This section contains information that does not change between releases.

Period-specific information

Time of recording – number of working days

There were 20 working days in January 2012, compared with 19 working days in January 2011.

New Zealand Harmonised System Classification

From January 2012 overseas merchandise trade data is compiled using the Harmonised System classification (HS2012). Before January 2012, the 2007 Harmonised System classification (HS2007) applies.

See the Excel supplementary table in the 'Downloads' box for a summary of the impact of this change on the overseas merchandise trade data.

The classification change means data users need to take care when analysing time series data, although changes from this review are not as significant as when HS2007 was introduced. The supplementary table uses the HS2012 classification to estimate January 2011 for comparison. Some assumptions had to be made to do this, so the results are not perfect, but the process almost removes the effect of the classification change from the data.

The release of the January 2012 trade statistics implements the latest five-yearly major review of the Harmonised System (HS2012). HS2012 replaces the 2007 version (HS2007). We will use HS2012 within overseas merchandise trade statistics until the next five-yearly review in 2017. Minor amendments may still occur on a quarterly basis.

Although the classification change potentially affects the published seasonally adjusted and trend series, our investigations so far show a negligible effect. We will communicate any effects we find when conducting our normal seasonal adjustment or trend series review processes.

Implementing HS2012 will also affect the overseas trade indexes (OTI). However, due to the way the OTI is calculated, the full effect of the change will not be implemented until the September 2013 quarter.

For more information on how HS2012 has affected overseas merchandise trade data, see Harmonised System 2012 and trade statistics.

For information about the HS2012 classification, see Harmonised System 2012.

General information

Merchandise trade – data source

Data is obtained from export and import entry documents lodged with the New Zealand Customs Service (NZCS). The data is processed and passed to Statistics NZ for further editing and compilation. Exports are compiled by date of export and imports are compiled by the date each entry passes through NZCS.

Export values given in foreign currencies are converted by Statistics NZ into New Zealand dollars, using weekly exchange rates when the statistics are compiled. For exports, a rise in the New Zealand dollar has a downward influence on prices and, as a consequence, quantities and values reduce.

Import values are converted from foreign currencies when import documents are processed by NZCS. The exchange rates used are set by NZCS each fortnight. These rates are prepared 11 days before the start of the fortnight, so have a lag of 11 to 25 days compared with the daily rates published by the Reserve Bank. For imports, a rise in the New Zealand dollar has a downward influence on prices and an upward influence on quantities. The combined influence on values can be either positive or negative.

Crude oil imports – effects of timing of recording

Imports are generally compiled by date-of-entry clearance by NZCS. NZCS entries are required from up to five days before, to 20 working days after, arrival of goods into New Zealand. The exception to this rule is for crude oil imports, which can have entries lodged later than 20 working days after entry into New Zealand.

Crude oil values for the latest month are estimated using actual quantities and country-of-origin data (provided by NZCS, based on information from the refinery at Marsden Point), together with estimated prices. These estimates for crude oil are replaced once actual entries are lodged with NZCS.

While all entries are provisional for the latest three months, and have the potential to be changed by the importer/exporter within this period, changes are not common, and generally do not have a material impact on the results. However, New Zealand has only a few ships carrying crude oil arriving each month, and each ship represents a high proportion of the monthly total of imported crude oil. Any variation in the data for crude oil resulting from a later lodgement date can result in a significant revision to the value. Once actual lodgements are received by Statistics NZ from NZCS, the value for crude oil can be regarded as robust.

Exports – timing of recording and undercoverage

From 1 March 2004, NZCS has not allowed goods to be loaded for export until an export entry has been lodged and cleared. A study undertaken in 2001/02 indicated that export entries not being lodged might account for between 1 and 3 percent of exports at that time. There is a possibility that the change in NZCS processes may have reduced this undercoverage, although this has not been quantified.

Seasonally adjusted series

Seasonally adjusted series are calculated monthly and for calendar quarters using X-12-ARIMA, which adjusts for outlying values and uses a centred moving average.

Seasonal adjustment removes the estimated impact of regular seasonal events, such as pre-Christmas purchasing, from time series. This makes the figures for adjacent periods more comparable. Seasonally adjusted figures are estimates and are subject to revision each period, with the largest changes generally occurring in the latest periods.

See Seasonal adjustment in Statistics New Zealand on the Statistics NZ website for more information.

Trend series

Time series can be split into trend, seasonal, and irregular components. Seasonal adjustment removes the seasonal component, while trend estimation removes the seasonal and irregular components. Trend estimates reveal the underlying direction of movement in a series and are used to identify turning points.

The trend series are calculated using X-12-ARIMA. The length of the centred moving average is selected automatically and can be 9, 13, or 23 months, depending on the relative variability of the irregular component compared with the trend. A long moving average has the effect of smoothing the trend series but slowing the response to underlying changes in growth rates. A short moving average produces a trend series that is less smooth but quicker to identify turning points.

To improve estimation of the underlying movement, the imports trend is calculated after removal of individual import items that have cif values of $100 million or more, such as large aircraft and ships. The trade balance trend is calculated by subtracting the imports trend from the exports trend.

Trend figures are recalculated each month. Using new monthly data means that previously published trend estimates are revised. These revisions mainly affect the latest months and can be large if a trade value is initially treated as an outlier but is later found to be part of the underlying trend.

Petroleum and products group

The petroleum and products group does not have stable seasonality so cannot be calculated separately. However, the change can be inferred by comparing the trend in total imports with imports excluding petroleum and products.

Broad economic category groups

Broad economic category (BEC) groups are arranged, as far as practicable, to align with the System of National Accounts’ three basic classes: capital goods, intermediate goods, and consumption goods. Commodities in BEC groups are categorised on the basis of their main end use. This means, for example, that all video recorders are treated as consumption goods even though some are used in business. Similarly, all helicopters are treated as transport equipment even though some are military goods (and are treated as such in the national accounts).

Standard International Trade Classification

The Standard International Trade Classification (SITC) is an output classification, which uses Harmonised System (HS) codes at the six-digit level as building blocks. It was designed by the United Nations as an analytical tool for economic analysis, which includes some simple implications regarding level of processing. Published figures are at a high level of aggregation; more disaggregated information is available on Infoshare. For customised jobs using the SITC Rev 4 classification, contact customer services at:

Overseas merchandise trade (OMT) statistics are compiled in close accordance with the United Nations' International Merchandise Trade Statistics Concepts and Definitions. OMT data, after adjustment, is used in the balance of payments and national accounts. The adjustments are for coverage, timing, valuation, and classification, and are explained in Balance of Payments – Sources and Methods 2004.

Confidential items

Under Section 37A (d) of the Statistics Act, the Government Statistician may disclose details of external trade, movement of ships, and cargo handled at ports. However, Statistics NZ understands that the release of merchandise trade commodity information can, in some cases, place commercially sensitive information in the public domain. Statistics NZ is able to provide a limited form of confidential status for commodity items (at the discretion of the Government Statistician), upon application by a company or business.

In practice, all confidential HS codes are aggregated into the code 9809.00.00.00 in order to protect their confidentiality and to maintain total export and import values. Any aggregations of HS codes below this level, which encompass confidential 10-digit codes, exclude the confidential value(s) for these codes.

The only aggregates that include the confidential codes are total exports, total imports, and the total exports and imports by country.

More information

More information about Overseas Merchandise Trade is available on our website.


While all care and diligence has been used in processing, analysing, and extracting data and information in this publication, Statistics NZ gives no warranty it is error-free and will not be liable for any loss or damage suffered by the use directly, or indirectly, of the information in this publication.


Timed statistical releases are delivered using postal and electronic services provided by third parties. Delivery of these releases may be delayed by circumstances outside the control of Statistics NZ. Statistics NZ accepts no responsibility for any such delays.

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