Overseas Trade Indexes (Prices and Volumes)

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The Overseas Merchandise Trade Prices and Volumes Indexes measure changes in the levels of prices and volumes of imports and exports of merchandise trade to and from New Zealand.

The Overseas Services Trade Price Indexes measure changes in the levels of prices of imports and exports of services trade to and from New Zealand.


The purpose of the Overseas Trade Indexes is to provide statistical information on how import and export prices and volume levels have changed between time periods, i.e. quarterly and annually.

The Overseas Services Trade Price Indexes measure changes in the levels of prices of imports and exports of services trade between New Zealand and the rest of the world.

Citation Information


Overseas Trade Indexes (Prices and Volumes)

Alternate Title

OTI, Volume, Prices, and Terms of Trade


Statistics New Zealand: International Business Performance Statistics (Volumes) and Prices (Prices)


Statistics New Zealand


Statistics New Zealand

Coverage Information

Temporal Coverage

  • 1981 to present

Topical Coverage

  • International trade and balance of payments



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Technical Report

Technical Reports


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Significant events impacting this study series

1915 - Export price index numbers made a first semi-official appearance in an article in the 1915 Yearbook.

1920 - An official export series going back to 1890 appeared in "Prices 1891-1919."

1924 - The Export Price Index was revised. Monthly and annual indexes used the Paasche formula on a 1909-13 (=1000) base (i.e. the weights used, related to values in the current period). The 25 commodities covered accounted for approximately 95 percent of total exports by value.

1933 - The Export Price Index was modified because an uneven collapse of prices in 1932 caused fluctuations. The weight allotted to each item included in the modified series, was the average quantity of that item exported during the previous five export seasons (i.e. years ended June). An Import Price Index, which included 220 items covering about 75 percent of the total value of imports, was produced. In the heterogeneous groups (e.g. drapery) a few specific items, for which import prices could be obtained, were regarded as representing price movements in the groups. The index was on a base of 1926 (=100) and was compiled annually on an All Groups basis (Laspeyres).

1942 - A revised Import Price Index based on, and using, the commodity weighting pattern of the three years 1936-38, and worked back to 1926, was constructed. Of the 240 items used in the calculations, about 10 percent were not import unit-values, but unit-values of other countries' (mostly United Kingdom) exports to New Zealand, or wholesale price quotations. Class weights were used to impute, to the unpriced items in a class, the same price movement of the priced items. This index was continued until 1949.

1950 - In 1949 a new and greatly enlarged commodity classification was adopted for New Zealand trade statistics, and this led to the construction of a new Import Price Index, which was calculated quarterly as well as annually. For 1950 and subsequent years, an annual index was obtained on base: the previous year, as the geometric mean of two indexes calculated respectively by using the weighting patterns of the two years (i.e. previous and current) being compared. Each annual index was then linked to that for the previous year. Thus, the index was of the chain-linked Fisher Ideal type.

1953 - The expression base of the December year 1953 (=100) was adopted for the Overseas Terms of Trade Index. The series was previously expressed on a 1936-38 base of 100.

1955 - The Standard International Trade Classification (SITC) was adopted for the presentation of New Zealand trade statistics, from the beginning of 1955. The number of export items priced was 60, which accounted for 95.4 percent of the total value of exports of New Zealand produce (other than wool), in the base period. Information for wool came from the Wool Price Index, which was based on auction prices. The new expression base was the December year 1952 (=100). The new series of export price index numbers were calculated for all periods from the first quarter of 1950, including the year ended June 1950. To obtain long-term comparisons, the old and new series were linked for the various groups, with links made through the December year 1950 and the year ended June 1950. The linked series were calculated back to the year 1914.

1959 - The Overseas Terms of Trade Index series was rebased in each of the years 1953 to 1958, with the latest year's index set to 100. In 1959, the fixed expression base of the December year 1957 (=100), was adopted. This expression base was retained until 1989.

1961 - Exports - With the introduction of a new weighting pattern, the December year 1960 (=1000) was adopted as the standard expression base for the long-term series. The series on the 1952 base, to which the older series on the 1909-1913 base had already been linked, were converted to the new base. Imports - A new series on base: December year 1959 (=1000), commenced. It was decided to continue the method used to calculate the annual index, but the quarterly index was calculated using the weighting pattern of the previous year only, and then linked on to the index for that year. A major change was that from 1959, the price index was designed to reflect changes in the true c.i.f. cost of imports.

1971 - Export and Import Price and Volume Indexes were revised, with the chain-linked Fisher Ideal Index calculation methodology also adopted for exports. The June year 1971 (=1000) expression base was adopted for both exports and imports. Wool data, as recorded on export documentation, replaced data derived from the Department's Wool Price Index. As from the September 1971 quarter, the Overseas Terms of Trade Index was calculated as the ratio of the two Fisher Ideal indexes of export and import prices. The expression base remained the December year 1957 (=100). The choice of base was arbitrarily made at the time it was adopted and was not intended to indicate that 1957 was a normal or standard year. It was considered desirable to retain the customary expression base to avoid confusion in the use of this key series.

1982 - A revised method of computer processing of the External Trade Price and Volume Indexes commenced with the September 1982 quarter indexes, following a review of the methods used in calculating the indexes. The basic methodology of chain-linked Fisher Ideal indexes was retained, but improvements were effected in timeliness of release and the statistical quality of the indexes. The expression base of the price and volume indexes was changed to the June year 1982 (=1000), although the Overseas Terms of Trade Index remained on the December year 1957 (=100) base. The range of available indexes was also extended.

1988 - The External Trade Price and Volume Indexes were renamed the Overseas Trade Price and Volume Indexes.

1989 - The Harmonised System (HS) for classifying overseas trade was introduced on 1 January 1988, replacing the separate export and import SITC Revision 2 classifications. Comprehensive links between the old classifications and the HS were established to ensure the continuity of the published trade index series during the March 1988 quarter to June 1989 quarter changeover period. Calculation of the Overseas Trade Price and Volume Indexes directly from data in the 10 digit HS format, commenced with the September 1989 quarter indexes. The range of published index series was revised. Some series were discontinued and some introduced, others were partially respecified to more closely reflect the commodity groupings of the HS classification, or to better reflect New Zealand's major export and import commodity groupings. The expression base of the price and volume indexes was changed to the year ended June 1989 (=1000). The expression base of the quarterly and annual Overseas Terms of Trade Index series was also changed, from December year 1957 (=100) to base: the average of the ten years ended June 1989 (=1000).

1992 - A range of import indexes by Broad Economic Categories (BEC), which group commodities by main end-use, and also aggregate to the three main categories of capital goods, intermediate goods and consumption goods, was released on INFOS and added to the Hot Off The Press release. Some series commence with September 1982 quarter and June 1982 annual indexes, some with September 1989 quarter and June 1989 annual indexes. For each export price and volume index grouping, related quarterly and annual f.o.b. dollar-value series were made available on INFOS. For each import index grouping, related c.i.f. value series were released on INFOS. Quarterly series commence with September 1989 quarter dollar values, June annual series with June 1990 year values, December annual series with December 1990 year values, and March annual series with March 1991 year values.

1998 - The merchandise export indexes and values were revised from September 1997 quarter to the December 1998 quarter. The merchandise import indexes and values were revised for the June 1998 quarter and the September 1998 quarter, to include updated data.

1999 - The Overseas Services Trade Indexes were added to the suite of Overseas Trade Indexes. The indexes use a building block structure and aggregate to the four published import and export categories as well as total imports and exports of services. A terms of trade for services is also calculated. The series' commence from the June 1997 quarter with an expression base of the June 1997 quarter (=1000). The series' are available on INFOS and added to the Hot Off The Press release.

2002 - Responsibility for the production of the price and volume indexes was separated. The Inflation Measures Division became responsible for the price indexes, while responsibility for the volume indexes remained with the International Accounts Division. The merchandise export price and volume indexes and values were revised from the September 1997 quarter to the September 2001 quarter. The revised data reflects: efforts by the New Zealand Customs Service to improve the export documentation completed by exporters a parallel export quality assessment by Statistics New Zealand a downward revision to butter export values to correct previously overvalued prices that included the tariff into the United Kingdom further editing of prices used in index calculations re-linking to more accurate annual indexes for the year ended June 1998.

2003 - The Overseas Trade Indexes were redeveloped in 2003, as a result of a project started in 1999.

The redeveloped series were first released in December 2003. The main outcomes of the redevelopment are;

  • The Fisher Ideal index formula is retained.
  • The price reference period and linking period are now the June quarter of each year (previously they were the June year).
  • An annual weight reference period has been adopted for the Paasche component of the index (this was previously quarterly).
  • Expenditure weights are being assigned at a lower level (the 10-digit Harmonised System (HS) item by country level; previously these were assigned at the 10-digit HS item level).
  • Imports valued on a New Zealand dollar value for duty (vfd) basis are now being used (previously the indexes used cost, insurance and freight (cif))
  • Unit values derived from administrative dollar value and quantity data collected by the New Zealand Customs Service have been selectively supplemented with prices collected directly from importers and exporters and by international price indexes.
  • For existing index categories, the originally published and redeveloped indexes have been linked at the June 2002 quarter, to provide continuous long-term time series.
  • All index time series have been re-expressed on a base of the June 2002 quarter (=1000). The June 2003 provisional quarter was the last quarter calculated using the old methodology, providing a one-year overlap with the new series.

2011 - The Overseas Trade Indexes (Prices): December 2010 quarter (provisional) and the Overseas Trade Indexes (Volumes): December 2010 quarter (provisional), were released one week earlier than usual. They are now released within 9 weeks of the end of the reference period. Previously they were released within 10 weeks of the end of the reference period.

2015 - In June 2015, the Overseas Trade Indexes (Prices) and Overseas Trade Indexes (Volumes) releases were combined into one Information release - Overseas Trade Indexes (Prices and Volumes): March 2015 quarter.

Usage and limitations of the data

Overseas Trade indexes are a Tier One statistic.

The OTI indexes are used as an inflation measure (quarterly and annually). Terms of Trade is a measure of the purchasing power of New Zealand's exports abroad, and is widely used by both public and private sector.

OTI source most of its data from overseas merchandise trade data. Overseas merchandise trade reports values while OTI gives the prices and volumes component. Volumes are calculated by dividing values by the price index. Volumes show the level of how much is exported or imported. This separates out the contribution of price movements to value movements to give the real movement.

Main users of the data

Central Government

Trading Banks

Economic analysts


3) Quarterly

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