UNIT VALUE AND PRICE INDEXES
8.14 There are two indexes that can be produced to reflect changes in export and import prices: unit value indexes based primarily on customs declarations 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 exports and imports 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.