3. The Price and Volume of International Trade: Background, Purpose, and Uses of Export and Import Price Indices

International Monetary Fund
Published Date:
December 2009
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A. Background and Origins of Price Indices

3.1 The purpose of this brief historical survey is to place the contents of this Manual in a longer-term perspective and to show that the measurement of price changes, or inflation, has long been recognized to be theoretically challenging as well as practically important.

3.2 Price indices are used for a variety of different purposes. There is general public interest in knowing the extent to which the prices of goods and services have risen. Also, it has long been customary in many countries to adjust levels of wages, pensions, and payments in long-term contracts in proportion to changes in relevant prices, a procedure known as index linking or contract escalation. Price indices have a long history for this reason.

3.3 A very early example is a simple index compiled by William Fleetwood in 1707, which was intended to estimate the average change in the prices paid by Oxford University students over the previous two and half centuries. Another 18th century example is an index compiled by the legislature of Massachusetts in 1780 to index the pay of soldiers fighting in the Revolutionary War against England (see Diewert, 1993a, for an account of the early history of index numbers).

3.4 During the 19th century, interest in price indices gathered momentum. In 1823, Joseph Lowe published a study on agriculture, trade, and finance in which he developed the concept of a price index as the change in the monetary value of a selected set, or basket, of goods and services, an approach still used today. He also noted the various uses for a price index, such as the linking of wages and rents, and the calculation of real interest. Diewert (1993a) argued that Lowe can be considered “the father of the consumer price index.” Later in the 19th century, further important contributions were made, including those of Laspeyres (1871) and Paasche (1874), whose names are associated with particular types of price indices that are still widely used. Marshall (1887) advocated the use of chain indices, in which indices measuring price movements from one year to the next are linked together to measure price movements over longer periods of time.

3.5 During the 1920s, several important developments occurred. In 1922, Irving Fisher published his monumental work, The Making of Index Numbers. This was prompted by Fisher’s interest in inflation and his advocacy of the quantity theory of money, in which changes in the money supply were held to lead to corresponding changes in the price level. A good measure of changes in the price level was needed—that is, a good price index—which led him into a systematic investigation of the properties of hundreds of different kinds of possible formulas for price indices.

3.6 Fisher’s preferred index, the geometric average of the indices advocated by Laspeyres and Paasche, is now known as the Fisher index. As summarized in Chapter 1 of this Manual, the Fisher index (or the closely related Törnqvist index) remains the preferred measure from a theoretical point of view for most purposes. From the perspective of the economic approach to index number theory, these indices have been shown in most circumstances to provide an unbiased estimate of changes in the cost of living for consumers and for price changes for firms that maximize revenue and minimize costs. The full details of the economic approach to the export and import price index (XMPI) are discussed in Chapter 18. The Fisher index number formula can also be justified from the perspective of averaging two equally plausible fixed-basket index number formulas (the Laspeyres and Paasche formulas), and this justification is presented in Chapter 16. The Fisher index also has a strong justification from the viewpoint of the test approach to index number theory, which is discussed in Chapter 17. The Törnqvist formula can also be justified from the viewpoint of the stochastic approach to index number theory, which is also discussed in Chapter 17.

3.7 In 1924, Konüs published a seminal paper laying down the foundations for the economic theory of the cost-of-living index, or COL index. A COL index is designed to measure the change in the cost of maintaining a given standard of living (or utility or welfare) as distinct from maintaining sufficient purchasing power to buy a fixed set of goods and services. In reality, consumers do not go on purchasing the same set of goods and services over time but adjust their expenditures to take account of changes in relative prices and other factors. The producer counterpart to the consumer’s cost-of-living index is the fixed-input output price index. This economic approach to the theoretical foundations for the XMPI was not fully developed until the 1970s: see Fisher and Shell (1972), Samuelson and Swamy (1974), and Archibald (1977). This approach is pursued in Chapter 18.

3.8 In 1926, Divisia published a paper in which he proposed price and quantity indices that factor the change in the monetary value of some aggregate flow of goods and services over time continuously and instantaneously into its price and quantity components. Although Divisia’s approach to index number theory is not immediately applicable, because price and quantity data are not available on a continuous basis, the Divisia index is useful conceptually when one has to choose between fixed-base indices or chained indices. The Divisia index and its connection with the chain principle for constructing index numbers are discussed in Chapter 16, Section E.

3.9 Thus, by 1930 the theoretical foundations (from all of the above perspectives) for the compilation of price indices, including XMPIs, had been laid. Although there were many refinements to index number theory from both an economic and a statistical viewpoint during the mid- and late 20th century, the essential elements were already in place early in the century. Developments in index number theory and practice over the past few decades are dealt with in detail in various chapters in this Manual and will not be summarized here, except to note that all of the above approaches lead to a very small number of index number formulas as being designated “best.” In particular, the Fisher formula emerges as being “best” from the perspectives of the economic, test (axiomatic), and averaging of fixed-basket indices approaches, whereas the Törnqvist formula emerges as being “best” from the perspectives of the economic and stochastic approaches.

B. Official Price Indices

3.10 As noted, there has always been considerable interest in, and demand for, price indices from the general public as well as governments. The 1780 index, referred to in the previous section, was specifically commissioned by a government agency in order to adjust the pay of soldiers in its employment. It is now generally acknowledged that governments have an obligation to provide the community and not merely themselves with information about price movements in the economy. A price index is a public good.

3.11 The practice of index-linking wages has a long history. Index linking means that the wage rate or material costs are adjusted in proportion to the change in some specified price index, the purpose being to maintain the real purchasing power of wages over the kinds of goods and services typically consumed by wage earners. As explained later in this chapter, an important use of XMPIs is to make adjustments in long-term contracts for changes in material costs. For such applications the specification of the index that is to be used can be a matter of some controversy. Whatever the exact formula used, index linking has important financial implications both for those making and for those receiving the payments in question. This in turn implies that there is a need for impartial, independent, objective, reliable, and credible price indices. The responsibility for compiling price indices must therefore be entrusted to a statistical agency that has both sufficient resources and the necessary independence from pressure groups of various kinds. This provides a second reason governments find themselves under an obligation to compile and publish price indices, or at least to supervise and monitor whatever agency is entrusted with the responsibility.

3.12 In practice, the government agency that is given the responsibility to compile and publish XMPIs is usually the statistics office or bureau, the central bank, or the customs authority (for goods exports and imports only). The central bank may be entrusted with the task of compiling XMPIs because in open economies the export and import prices are important determinants of domestic inflation, which most central banks want to control using the instruments of monetary policy.

3.13 Price indices for industrial commodities also have a long history. In Canada, a wholesale price index (WPI) of 89 commodities was compiled using an unweighted geometric mean for the period 1867–90. After that, the index was expanded to cover more commodities and to use a Laspeyres index. The first industrial commodities index in the United States was produced in 1902 (covering the period 1890–1901), using an unweighted average of price relatives for about 250 commodities. This index was developed in response to a U.S. Senate Finance Committee request for an investigation into the effects of tariff laws on prices of domestic and foreign agricultural and manufactured products. A system of weighting was first used in 1914. The original index was also referred to as the WPI because it covered commodity prices before they reached retail markets.

3.14 In Europe, the first WPI for the United Kingdom was prepared by the Board of Trade and presented to Parliament in 1903. The price reference year was 1871, and the series covered the years from 1871 to 1902. The prices were mainly derived from the trade accounts, with weights estimated from different commodities used, or consumed, in the country between 1881 and 1890. This index covered of 45 commodities, mainly basic materials and foodstuffs. Following World War II, a number of countries also began collection of data on wholesale prices of commodities in an effort to measure price changes at an earlier level in the production process. Around 1970 Eurostat, the Statistical Office of the European Union (EU), began a systematic program to encourage members to collect industrial output prices in an effort to get information on prices as products left producers’ factories. These price indices were thus called producer price indices—PPIs—because they attempted to measure the change in prices producers received at the factory gate. In the past 5–10 years, many national statistical agencies have been progressively extending coverage of their national PPIs to measure changes in service industry prices, which in many countries now account for nearly two-thirds of GDP.

3.15 PPIs usually are compiled monthly, although some countries compile them only quarterly. Countries also try to publish them as soon as possible after the end of the month to which they refer, sometime within two weeks of the reference month. Moreover, most countries prefer not to revise them once they have been published. In contrast to many other kinds of statistics, most of the required data, at least on prices, can be collected at the same time.

3.16 PPIs have two characteristics that users find important. They are published frequently, usually every month but sometimes every quarter. They are available quickly, usually about two weeks after the end of the month or quarter. PPIs tend to be closely monitored and attract a lot of publicity. In many countries the PPI is not revised once it is published, which is viewed as an advantage by many users.1

3.17 The export and import price indices usually are thought of in connection with customs records, because these have traditionally been the main source of information. These records pertain only to goods in almost all countries, as well as the shipping and insurance services involved in the transport of imports. As such, they traditionally have been compiled for goods as indices of the unit values of detailed customs classes. As discussed in Chapters 2 and 5, detailed customs goods classes rarely contain only one product. Thus unit values will suffer from composition effects, wherein the product composition of the unit value for a given customs class varies from period to period. This can cause the unit value price relative from period to period to change even if the prices of the component products have not. Thus the unit value price index tends to be biased in unpredictable directions. Of course, bias in one direction of the unit value price implies bias in the opposite direction of the customs volume index. Comparisons with survey-based data illustrate the extremely volatile nature of unit value indices (see Chapter 2). Further, with customs unions, inter-area trade data will generally not be available.

3.18 As a result, a number of countries have discontinued computing the price relatives as unit values for some or all of the detailed classes of their XMPIs and for some countries of origin/destination. They instead directly survey establishments engaged in international trade to record the prices received by exporters and paid by importers to form the detailed price relatives and indices comprising their XMPIs.2 Customs unit values and these surveys are the subject of Chapters 2 and 6.

C. International Standards for Price Indices

3.19 Once a statistic is accorded official status and given some prominence, the establishment of international standards usually follows. International standards are needed for several reasons—and not merely in order to compile internationally comparable statistics. The first international standards for XMPIs were promulgated in 1981 by the United Nations (UN). The UN Statistical Commission at its nineteenth session requested the preparation of manuals on the practical aspects of collecting and compiling price and quantity statistics within the overall framework of the “Guidelines on Principles of a System of Price and Quantity Statistics,” which was issued in 1977. The United Nations Statistical Office released the “Manual on Producers’ Price Indices for Industrial Goods” in 1979 to provide practical guidance on the preparation of industrial PPIs, and “Strategies for Price and Quantity Measurement in External Trade” was released in 1981 to provide guidance on XMPIs.

3.20 This Manual discusses revised and updated methods for XMPI compilation based on current practice and recent developments in price index number theory.

3.21 Some international statistical standards are developed primarily to enable internationally comparable data to be collected and published by international agencies, such as the statistical offices of the United Nations, the International Labor Office (ILO), the International Monetary Fund (IMF), or the Organization for Economic Cooperation and Development (OECD). The publication of such data by an international agency is often seen as a guarantee that the data conform to internationally accepted standards even though this may not always be the case in practice. Although national statistical offices actually supply the data to the international agencies, their publication by the international agencies is often interpreted as a public endorsement of their reliability, which enhances their status and credibility even within their own country.

3.22 However, international standards are not developed simply to enable internationally comparable data to be compiled. Many countries choose to use them as norms or standards for their own statistics. In this way, small national offices with limited resources of their own benefit from the collective views and experience of experts from a wide range of countries on which the international standards are based.

C.1 Current revision

3.23 This Manual has been developed in response to several factors. A considerable amount of work on the methodology of price indices, covering both theoretical issues and optimal methods of calculation, was undertaken at an international level during the 1990s as a result of the formation of an international group of price experts. This group, the International Working Group on Price Statistics, established under the auspices of the United Nations Statistical Commission, met for the first time in Ottawa in 1994 (and is therefore called the “Ottawa Group”). It brought together leading experts on price indices from national statistical offices and universities from around the world. During the course of its seven meetings through 2002, well over a hundred papers on the theory and practice of price indices were presented and discussed. This collective activity at the international level has inevitably led to some rethinking about, and elaboration of, the previous international standards on consumer price indices (CPIs), PPIs, and XMPIs as embodied in the ILO Manual on Consumer Price Indices (Turvey and others, 1989), the Manual on Producers’ Price Indices for Industrial Goods (UN, 1979), and Strategies for Price and Quantity Measurement in External Trade (UN, 1981). This current XMPI Manual also incorporates approaches to the measurement of prices of exports and imports for services.

3.24 Another factor is the high priority accorded to the control of inflation as a policy objective in most countries, after the experience of high, or even hyper, inflation in the past three decades of the 20th century. The slowing of inflation in many parts of the world in the 1990s, compared with the 1970s and 1980s, far from reducing interest in its measurement, has stimulated a demand for more accurate and reliable measures of inflation. Whereas an error or bias of 1, or even 2, percentage points in the annual rate of inflation may not be considered so important when inflation is running at 10, 20, or more percent, it becomes very significant when the rate of inflation itself is estimated to be only 1 or 2 percent. Inflation may slow down to the point at which it is not even clear whether prices are rising or falling, on average.

3.25 The need for a revised manual on XMPI compilation, as was the case of the PPI revised manual, followed from concern over CPI measurement issues. Users of CPIs in some countries have become convinced that the indices are subject to an upward bias, mainly as a result of their failing to make proper allowance for improvements in the quality of many goods and services, especially newer goods, such as computers, that are subject to rapid technological progress. The treatment of changing quality has long been recognized as particularly difficult on both conceptual and practical grounds. This topic has been intensively investigated, with numerous new studies on the subject appearing in the 1990s.

3.26 It has also been realized that, because of the widespread use of price indices for the index linking of social benefits, such as pensions and other government payments, and as an escalator for price adjustments to long-term contracts, the cumulative effects of even small potential biases can have considerable financial consequences for government budgets and private industry purchases over the long term. This has led to governments themselves scrutinizing the accuracy and reliability of price indices more intensively than in the past.

3.27 Within the European Union, the convergence of inflation was deemed to be an important prerequisite for the formation of a monetary union. This requires precisely defined price indices that are comparable among countries. An intensive and prolonged review of all aspects of the compilation of CPIs was undertaken during the 1990s by all the national statistical offices of the member countries of the European Union in collaboration with Eurostat. This work culminated in the elaboration of a new set of international standards for the 29 member and candidate countries of the European Union and led to the development of the EU’s Harmonized Indices of Consumer Prices, or HICPs. Work on the HICPs proceeded in parallel with that of the Ottawa Group, many of whose experts also participated in the development of the HICPs.

3.28 The need for revising the ILO manual to incorporate these new developments was one of the major recommendations at the 1997 joint United Nations Economic Commission for Europe (UNECE)/ILO meeting on the CPI. Similarly, the Inter-Secretariat Working Group on Price Statistics (IWPGS) came to the conclusion that a new PPI manual was long overdue as well as a manual on XMPIs.

3.29 Significant developments have taken place in the practice of price index construction that now necessitate a revision of the 1981 UN manual. Among these are emergence of the economies in transition, increased inflation, the reality that XMPIs may overstate inflation even when international standards are followed, the need for constructing and publishing more than one index to meet specific requirements (e.g., XMPIs by destination country of export and source country of import), and so on.

C.2 Responsibilities of the international agencies

3.30 The traditional practice of index linking wages and contracts in many countries has meant that, at both a national and an international level, ministries or departments concerned with economic policies and statistics have taken responsibility for price indices. However, many government departments—especially ministries of finance, economics, industry, and trade, and of course central banks—are concerned about inflation and have acquired an interest in a variety of price indices as key indicators of inflation and its transmission.

3.31 All the international agencies concerned with general economic policy now attach importance to XMPIs and their movements. In addition, Eurostat, the ILO, the IMF, the OECD, the World Bank, the UNECE, and the World Trade Organization (WTO) all have a strong interest in XMPIs. Some of these agencies have provided technical assistance in the compilation of XMPIs to countries in transition as well as to developing countries. The agencies therefore agreed to pool their resources and collaborate in the present revision of the Export and Import Price Index Manual (XMPI Manual), using the IWGPS to manage the process.

C.3 Links between the new CPI, PPI, and XMPI Manuals

3.32 One of the first decisions of the IWGPS was to produce a CPI and a PPI manual in parallel. Movements in producer prices are clearly important for the measurement of inflation and the analysis of the process of inflation within an economy. PPIs have been comparatively neglected, however. Whereas there has been an international manual on CPIs for more than 70 years, there has been a manual on the PPI covering industrial output for only about 25 years. Following the publication of those manuals in 2004, the IWGPS turned its attention to a manual on XMPIs to update the previous manual, which was published nearly 30 years ago.

3.33 This new Export and Import Price Index Manual was based, wherever appropriate, on the Consumer Price Index Manual (ILO and others, 2004a) and Producer Price Index Manual (ILO and others, 2004b). XMPIs and PPIs especially have a lot of methodology in common and this Manual draws heavily from the PPI Manual. Both draw on the same theoretical literature pertaining to index numbers. Whereas CPIs also draw on the economic theory of consumer behavior, both PPIs and XMPIs draw on the economic theory of production and the short-term rigidities in the production process.3 The economic theory of all of these indices leads to the same kinds of conclusions with regard to index number compilation. It was therefore decided that the IWGPS manuals should be similar in form and as consistent as possible, sharing common text when appropriate.

C.4 Inter-Secretariat Working Group and the technical expert groups

3.34 Responsibility for the production of the CPI, the PPI, and the XMPI Manuals rested with the same Inter-Secretariat Group consisting of staff from the statistical offices, departments, or divisions of the ILO, the IMF, the World Bank, the UN, the OECD, and the EU. Expert advice on the contents of the three Manuals was provided by three parallel technical expert groups consisting of invited experts on CPIs, PPIs, or XMPIs from national statistical offices and universities together with experts from the international agencies themselves. To ensure consistency, there was overlap of membership among the expert groups.

3.35 Most members of the technical expert groups also participated in meetings of the Ottawa Group, which supported the decision to revise the CPI Manual and to produce a new PPI Manual. The Manuals draw on the contents and conclusions of the papers presented at meetings of the Ottawa Group and the Voorburg Group, thus providing the outlets through which the groups’ conclusions can influence the actual compilation of price indices. In addition, the XMPI Manual has been drafted with notification to and comment from the Interagency Task Force on Trade Statistics, comprising the WTO, UN Statistics Division (UNSD), UNCTAD, the World Customs Organization (WCO), the UN Regional Economic Commissions, the Commission of the EU, and other agencies.

D. Purpose of Export and Import Price Indices

D.1 Background

3.36 The XMPIs are a weighted average of the price changes in groups of products between one time period and another. The average price change over time cannot be directly observed and must be estimated by measuring actual prices at different points in time. Price index numbers are compiled from the collected price observations through time; their significance lies in a series of index numbers referencing the comparison prices between a particular period and a reference base. For an index to provide information on price changes, at least two index numbers from the same series need to be available.

3.37 XMPIs do not attempt to measure the actual level of prices but measure the average change in prices from one period to another. Changes in the value of exports and imports are usefully, for economic analysis, decomposed into their price and volume components, and XMPIs are measures of the price component. XMPIs, as measures of the price change component, when divided into—that is, used to deflate—the change in their counterpart value aggregate, yield a measure of the change in volume terms.

3.38 Several different pricing concepts are used in price index measures and in foreign trade statistics. Among these are the basic prices received by producers, the purchasers’ price paid, prices reported as free on board (f.o.b.), and prices including cost, insurance, and freight (c.i.f.). Valuation differences in the observed prices will arise depending on which of these pricing concepts are applied. For example, a national statistical office using establishment survey data may produce XMPIs from a resident’s point of view and may value exports at basic prices (factory gate) and imports at purchasers’ prices. Alternatively, using customs data, exports may be valued f.o.b. and imports c.i.f. Differences in valuation are discussed in more detail in Chapter 4.

3.39 Relative prices are changing all the time, with some prices rising and others falling. Because price changes can vary considerably from product to product, the value of the price index will be dependent on the precise set of goods and services it covers. It will also depend on the weights attached to the different kinds of products within the set.

3.40 The goods and services coverage of the XMPI varies across the world, but almost all cover goods in international trade, as well as the shipping and insurance services supplied on imports. Other internationally traded services, such as business, information, and financial services, also are in scope for the XMPI. Compilers are including them in XMPIs as well as in PPIs and CPIs as international consensus forms on how to measure their prices and output.

D.2 Uses

D.2.1 Sources of inflationary pressure

3.41 As outlined in Chapter 15, the import price index (MPI) serves as one component of inflationary pressure, the other being the PPI, which covers supply from domestic production. Inflation can be imported as part of intermediate consumption (inputs) to establishments, capital formation, final demand by households, governments, and other institutions. The economic analysis of such issues as outsourcing requires detailed data on price changes of domestically produced and imported goods and services and switches from one to the other. Export price indices (XPIs) serve as an indicator of price changes of one component of the economy’s total output of goods and services, the other being that directed to the domestic market.

D.2.2 Terms of trade

3.42 Changes in the ratio of export to import prices have a direct impact on changes in the real income of a country. If the prices of a country’s exports rise faster (or fall more slowly) than the prices of its imports (i.e., if its terms of trade improve) fewer exports are needed to pay for a given volume of imports. Thus, an improvement in the terms of trade, or a trading gain, makes it possible for an increased volume of goods and services to be purchased by residents out of the incomes generated by a given level of domestic production—the real income of a country increases. The measurement of this terms of trade effect is outlined in the 2008 System of National Accounts (2008 SNA), Chapter 15 (Section C) and requires price indices of imports and exports. It is worth noting that there is a difference between changes in the volume of domestic production, as measured by GDP in volume terms, and changes in real gross domestic income (GDI), the latter including, unlike the former, trading gains (or losses) owing to terms of trade effects. The difference between movements in the volume of GDP and real GDI are not always small. If imports and exports are large relative to GDP and if the commodity composition of the goods and services that make up imports and exports is very different, the scope for potential trading gains and losses may be large. This may happen, for example, when the exports of a country consist mainly of a small number of primary products, such as cocoa, sugar, or oil, while its imports consist mainly of manufactured products. Chapter 24 of this Manual provides an alternative framework that benefits from being derived from the economic theory of price indices, as outlined in Chapter 18. It shows how the product of a superlative export price index and a superlative import price index can account for changes in the country’s real net (primary) income.

D.2.3 Government economic policy

3.43 Foreign trade indices are critical for government economic policy for several reasons. They enable the projection of budget figures and the forecasting of economic trends; they are essential for preparing negotiations with countries providing capital; and they help to conduct market surveys of strategic products.

3.44 Governments make regular projections in their budgets to determine the amount of additional revenue needed to finance current spending and investment programs. As a major component of government revenue, customs revenue is forecasted based on past trends in export and import values that make up the tax base. Understanding and forecasting value changes is facilitated by understanding and forecasts of the price and volume components. Forecasts of revenue can be made for individual product groups based on the principal duty rates. Government budget and public spending program forecasts are in principle always part of a macroeconomic framework representing the economic performance projections for different sectors (such as agriculture, industry, and services) to ensure that budget and public spending program forecasts are consistent with the economic activities in question.

3.45 Customs revenue is often central in the negotiations between governments and foreign capital providers. International agencies often extend loans on the condition that national authorities successfully meet macroeconomic targets, such as the size of the government deficit to GDP. Accurate information regarding international targets is thus essential, to the lender as well as to the authorities of the borrowing government. Accordingly, customs duties and foreign trade (prices and volumes) are closely monitored to ensure that the specified conditions on the flow of international finance are effectively met.

3.46 The breakdown of relative change over time of the value of exports and imports into price and volume components is needed to conduct economic analysis that supports the development of macroeconomic and international trade policy, and to disseminate information needed for effective decision making.

D.2.4 Analysis of competitiveness and productivity

3.47 An industry remains competitive only if its prices are kept in line with the market. Exporters have a critical interest in knowing the evolution of prices for products similar to their own from suppliers in other countries. On the other side of the market, importers also need to know about the evolution of the prices of the products they purchase to secure the least-cost source among supplying countries.

3.48 Studies of competitiveness involve analyzing the evolution of prices, not only in the domestic currency but also in the currencies of the country’s main trading partners. For example, a country’s stable export price index may mask a devaluation leading to higher competitiveness of the products that the country exports.4

3.49 Changes in the productivity of a sector can be measured in terms of changes in the ratio of the volume of net output to its primary inputs, or gross output to primary and intermediate inputs. Outputs and inputs need to be measured in volume terms and this in turn requires appropriate price deflators. The deflators for outputs include those for the domestic and export markets, and for inputs those from the domestic market and those imported—that is, the components of XMPIs.

D.2.5 Drawing up trade contracts

3.50 Businesspeople and potential investors may conduct market surveys on a particular product, in which they analyze corresponding supply and demand, so as to identify whether the product could be profitable for production or export purposes. To increase the accuracy of such an analysis, it requires more detailed information about the product, such as existing world sources of supply relative to potential demand, price, and identification of the main exporters and main national trading partners.

3.51 Import and export prices are used for contract escalation to ensure that the payment for some output or input is equal in real terms to what was agreed upon when the contract was signed. Appropriate import price indices can be used as an escalator for a long-term contract signed by a manufacturing firm to purchase production inputs from abroad. Likewise, appropriate price indices can be used as an escalator for a long-term contract signed by an exporter to deliver a product to a foreign buyer.

D.2.6 Measuring inflation, forecasting future price trends

3.52 Foreign trade indices are also a critical factor explaining the evolution of domestic inflation. Import prices affect the level of domestic inflation in several ways. Decreasing import prices of final goods directly affect the overall level of prices in the economy. Import prices can also be a good indicator of future inflation in a country where many inputs to domestic production are imported. Declining prices of imported inputs to manufactured goods have an indirect impact on the level of output prices by lowering the cost of production. More directly, if import prices for a product are falling, national producers of that product will have to lower their prices to preserve their competitiveness. Any seasonal or trend information embedded in the time series of import prices would contribute to the knowledge about future price levels.

D.2.7 Exchange rate analysis

3.53 To anticipate the effects of exchange rate adjustments, it is important to know the fraction of exchange rate movements that is passed on to the prices of exports and imports. The answer to this question depends on the extent to which the “law of one price” holds as well as on pass-through rates.5 Pass-through rates measure the percentage of exchange rate changes that are passed through to the prices of imports and exports. If a local currency appreciates against foreign currencies, import prices will no doubt fall while export prices should rise. A depreciation of the local currency would have the opposite effect. Pass-through rates are usually between zero and 100 but can be negative if a change in the exchange rate has the opposite effect on export or import price indices; these rates can exceed 100 if the export or import price index changes by a greater magnitude than the exchange rate.6 Changes in the ratio of export to import prices are of interest in determining exchange rate changes, especially for tradable as against nontradable goods and services.

D.2.8 Compilation of national accounts in volume terms

3.54 Import and export data are very important in the compilation of volume estimates of national accounts. This applies, in particular, if this compilation of national accounts is based on expenditure components or on product balances, as outlined in Chapters 4 and 15. Imports are among the sources of supply of products to the economy, whereas exports are among the uses of products The XMPIs used as deflators and the value aggregates for exports and imports must have prices valued on the same basis.

E. Family of XMPIs

3.55 As noted in Chapter 4, this Manual takes the position that there is, in principle, only one economic valuation and timing basis for international goods and services trade flows: the change of ownership basis of the 2008 SNA. By implication, the buyer becomes liable for the cost of the good or service at its transaction value on the date of change of ownership. Any tariffs or other taxes levied in the course of the item’s passage from source to destination, or any transport and distribution services, accrue on the date the importer or exporter becomes liable for the cost of them. The accrual dates for these services could differ from the change of ownership date of the good and, if different, generally would be later than that date. This is less important in domestic statistics than for international trade, because some commodities can lie in entrepot inventory for a considerable period before a final destination is set for them. XMPIs constructed on these principles are the definitive set.

3.56 The main recording system for trade in goods is customs documentation, typically tariff schedules, which captures the c.i.f. value of goods when they cross the frontier of the importing country. A customs agency records exports via declaration forms at the time the imports embark toward a foreign destination, or international waters. Customs documents usually also record a quantity relevant to customs administration (and also relevant to determining shipping costs), typically in units, weight, and/or cubic volume displaced in shipment. As such, the customs basis for recording represents an alternative set of value, price, and volume statistics for international trade to the economic basis of the international statistical standards of the 2008 SNA. For many types of goods, it may be qualitatively and quantitatively close to the standard. Compilers often use the customs basis estimates as a proxy for the economic concepts in the international standards, as outlined in Chapters 4 and 15.

3.57 When there are measured differences between the ownership-based and customs-based statistics, however, the ownership-based ones should prevail. Say there is a difference in the coverage of goods owing to the recording principles used for customs purposes, as against the desired ownership change principle. Then the customs-based price indices will serve as proxies for the ownership-based price indices if the price change of the trade arising from the difference in recording is similar to that of the price change of the measured customs-based trade. This follows from the fact that price indices are unaffected by changes in coverage, even if the excluded products are substantial, as long as the price changes of the excluded products are similar, on aggregate, to those of the included ones.

E.1 Industry aggregation

3.58 Breakdowns of the XMPIs by the industries of the reporting establishments assist us in gauging the impact of world price movements by domestic industry and facilitate constructing price indices for intermediate consumption in the national accounts.

E.2 Macroeconomic aggregations

3.59 High-level aggregations of the XMPIs, such as total exports and imports, contribute to the price index for GDP by accounting for the price change in net exports. Their direction of trade statistics—exports and imports by destination or source country, respectively—may also contribute to our understanding of how exchange rates and bilateral trading conditions affect the rates of change in export and import prices.

E.3 Commodity analysis

3.60 Analysis of MPIs by commodity reveals the sources of inflationary pressure from imports, which may be priced in international markets and thus outside the control of domestic agencies. Particularly important examples are the price change of crude oil and food. Aggregations of commodities can also be constructed to show the total impact of commodity price change on the economy. Analysis of the XPI by commodity contributes to our understanding of price pressures on domestic production capacity arising from changes in export demand. When the terms of trade are viewed as the relative rate of change in the prices of a country’s package of exports with its package of imports, commodity breakdowns allow us to see how world commodity price movements contribute to movements in the terms of trade for a given country. The analysis of the effect of outsourcing requires commodity-level data on the price changes of domestic and imported goods and services and, when it occurs, switches from one to the other. MPIs are but one component of the quite demanding data needs for the task.

E.4 Stage of production

3.61 A further method for analysis is to aggregate by stage of production, in which each commodity is allocated to the stage in which it is used. This differs from stage of processing because a product is included in each stage to which it contributes and not assigned solely to one stage. The classification of products to the different stages is usually achieved by reference to input/output tables in order to avoid multiple counting of the stages that are not aggregated. There is a growing interest in this type of analysis—for example, these types of indices are already compiled on a regular basis in Australia (see, for example, Australian Bureau of Statistics, 2001).7 The XMPIs may be broken down with the same classification by product stage of processing as the PPI.

E.5 Final expenditure price index

3.62 A further variant is the final expenditure price index (FEPI). This measures prices paid by consumers, businesses, and government for final purchases of goods and services. Intermediate purchases are excluded. XMPIs are used as proxies for the final prices paid for investment goods by businesses and government in the FEPI model used in Australia. This is because most XMPIs reflect changes in basic prices or producers’ prices (not purchasers’ prices). This topic is further considered in Chapter 6.

In many countries both the XMPI and consumer price index (CPI) are not subject to revision once published unless an error is discovered in price collection or compilation. In a number of countries, however, it is standard practice to revise the XMPI once more complete information is available. For example, in the United States the XMPI is revised with a three-month lag; that is, the most recent three months are preliminary (subject to revision), whereas the fourth month’s data are final.

Among the countries that are exceptions to extensive use of customs unit values in trade price indices are Australia, Czech Republic (partially), Estonia, Latvia (nonhomogeneous goods), Mauritius (partially), Singapore, Sweden, United Kingdom (manufactured goods), and United States. These countries instead make substantial use of price surveys of narrowly defined products. See United Nations (2005).

This is not strictly true because there usually is at least a small portion of expenditure on imports and receipts from exports that accrue directly to households as final consumption. A good example is “cross-border shopping,” which may be important in some countries. In this case, households may import by visiting a neighboring country where they buy goods and services and carry the goods or the result of the services back with them to their home countries. Exports can occur when the item purchased is a transportable durable good, such as an automobile. In this case, the transaction should be recorded as an import by the country of the purchasing household and as an export by the country of the selling household. If the durable is second-hand, because consumer durables are recorded in consumption on a net acquisitions basis, the import adds to the consumption expenditure of the importing country and subtracts equally from the consumption expenditure of the exporting country, leaving expenditure on GDP unchanged in both countries when the export and import effects are taken into account. If the durable is new, the export is subtracted from capital formation (change in inventories) if purchased from stock. Only if the durable is new and delivered directly to the buyer by the nonresident producer in the period it was produced will there be no offsetting negative final expenditure for the exporting country. See Chapter 15 for further discussion of the effects of international trade on final consumption expenditure.

In a country with the schilling as the national currency, exporting coffee to the United States, for example, the export price index in schillings (S) for coffee shows zero inflation because the price of a kilogram is constant at S 100 in successive years, whereas the export price index in dollars ($) shows a decline of 1.5 [(100/10)/(100/15]). This is because the exchange rate (S/$) increases (devaluation of the schilling) from $1 = S 10 in the first year to $1 = S 15 in the next.

The assumption of one price states that the price of an item, adjusted for tariffs and transport costs, is the same in all countries. Exchange rates account for differing price levels.

The pass-through rate for imports is the ratio of the import price index deflated by the average exchange rate index.

This topic is also considered in Chapter 15.

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