Quantity measurement

8.1 Quantity is an important dimension of international merchandise trade statistics. It is essential for various policy and analytical purposes including for the planning of transport infrastructure, the compilation of energy, agricultural and commodity statistics, assessing the impact of international trade on the environment, verifying trade values and compiling trade volume and price indexes.

8.2 This chapter will describe quantity measurement in Australia's international merchandise trade statistics, how the unit of quantity for a commodity is determined, the relationship between quantity and gross weight, and the difference between unit values and price indexes.

8.3 In 1995, the World Customs Organisation (WCO) adopted the use of standard units of quantity to promote international comparison and analysis of HS statistics. The WCO standard units of quantity are shown in Table 8.1 below.

8.4 In Australia's international merchandise trade statistics, the unit of quantity shown against a particular commodity code is that specified in the AHECC (8 digit level) or Customs Tariff (10 digit level) classification. Where feasible this is the WCO standard unit as specified in the HS. Where the WCO standard unit is not used for that commodity in the Australian industry, the unit of quantity will generally be the normal unit of quantity used for a particular commodity in the associated industry. For example, commodities which are exported in bulk have a unit of quantity of tonnes rather than kilograms.

8.5 In some cases, a single commodity code covers a diverse range of goods e.g. 'parts'. In these instances the unit of quantity is NR (Not Recorded) and quantity data are not provided.

8.6 For duty purposes and to meet the needs of users of the data, some commodities have second units of quantity. This is catered for in output by creating a companion tariff code against which only the second quantity is recorded. Only import commodity codes in Chapter 22 have a second unit of quantity, i.e. Litres (L) where the first unit of quantity is Litres of alcohol (LA).

8.7 Net weight is only recorded where that is the specified unit of quantity, but gross weight is recorded for all export transactions and all import declarations (see paragraphs 8.11 - 8.13 in the Quantity and Gross Weight section below). Conversion factors to the WCO standard units of quantity are not provided.

8.8 Where new statistical codes are added following a Classification Feasibility Study, the unit of quantity will be the WCO recommended unit unless it is not used or recognised in the Australian industry. In that case the unit of quantity will be determined in consultation with importers and exporters.

8.9 Table 8.2 below lists the units of quantity used in Australia's international merchandise trade statistics. Some of these units of quantity are used in historical output only (marked with an *).

8.10 Because the unit of quantity is recorded against the most detailed classification code, any quantity aggregation must be undertaken with care. For example, aggregating data for commodities with mixed units of quantity (as in the table below) will produce meaningless quantity totals.

8.11 Quantity is the measure of how many or how much of a commodity is imported or exported. A measure of quantity can include tonnes, kilograms, number, litres (and other units of measurement). Where quantity is recorded by weight e.g. kilograms, it does not include the weight of packaging. This is an important distinction from gross weight. Gross weight is the shipping weight of goods (measured in kilograms for ABS output) in the packaged state, excluding the weight of shipping containers. It includes the weight of moisture content, wrapping, crates, boxes and outside packages.

8.12 In Australia's merchandise trade statistics, net weight is not included on all transactions, except those where the unit of quantity is grams, kilograms or tonnes. Net weight excludes any outside packaging, inner containers or wrappings or any carrying medium (e.g. liquid) surrounding the goods.

8.13 Australia's international merchandise trade gross weight statistics are not used to estimate net weight. Gross weight is recorded for each commodity on a customs export declaration. For imports, gross weight is not recorded at the individual commodity level but total gross weight is reported for all the commodities on a customs import declaration. There is no reliable method to apportion gross weight to diverse commodities recorded within a declaration. ABS assign gross weight to one line/commodity on the declaration to enable commodity estimates to be produced. Therefore gross weight statistics for imports are only reliable when aggregated at the port or state level and not at the commodity level.

8.14 There are two indexes that can be produced to reflect changes in import and export prices: unit value indexes based primarily on customs documentation and price indexes based on survey data.

8.15 The average unit value of a commodity for any given period is the total value of shipments divided by the corresponding total quantity. This is often considered to be an average price at a given point in time but it represents the average unit value of a mixture of goods at a point in time.

8.16 Unit value indexes measure changes in the average unit value of individual commodities over time. The goods that comprise the shipments are not necessarily homogeneous and the indexes may be affected by changes in the mix of goods as well as by changes in their prices. For this reason unit value indexes may not provide a good measure of average price changes over time for groups of non-homogeneous goods. However, when goods are homogeneous and quality change is minimal (e.g. basic mining and agricultural goods) the index is more reliable.

8.17 The ABS does not publish average unit values or unit value indexes. Average unit values can be calculated from detailed commodity data released by the ABS but they should be used with caution as they are not a good measure of price change over time.

8.18 Price indexes for imports and exports using a variety of international classifications are published by the ABS in International Trade Price Indexes, Australia (cat. no. 6457.0). These indexes are primarily based on survey data but use international merchandise trade value and quantity information to calculate price movements for selected commodities, to identify units to sample and to derive weights for samples.