Gross Domestic Product

Gross national product (GDP) is a total of the outputs recorded in a country’s national accounts. It is the best-known of such totals, and estimates of its growth rate are widely used as indicators of the prospects of inflation or unemployment. Efforts are constantly being made to overcome its limitations for that and other purposes. GDP per capita (that is, divided by total population) is the most frequently used measure of a country's or region's level of economic development; for alternative measures, see Human Development Index.

Definitions

Gross domestic product (GDP) can be defined as the total recorded value of the goods and services produced within an economy. The word "gross" indicates that no deduction is made for the loss of value due to the depreciation of assets, and the word "domestic" indicates that net income from abroad is not included. (If income from abroad is allowed for, gross domestic product becomes gross national product (GNP), and if depreciation is also allowed for, it becomes net national product or simply national income).

GDP can in fact be defined as either the total recorded output of the economy’s producers, or the total recorded expenditure of its investors and consumers, or the total of all recorded payments of wages, interest and rent - all of which totals are, in principle, equal. It is normally stated as "GDP at market prices", which indicates that the prices used include the effects of indirect taxes and subsidies. In an alternative version that matches payments to the factors of production, indirect taxes (such as sales taxes) are deducted, and subsidies (which are the equivalent of negative sales taxes) are added back - and the adjusted total is then termed "GDP at factor cost". Published statistics normally include estimates of "GDP at constant prices", which are obtained by applying approximate price index adjustments to the recorded values of its components. Time-series thus adjusted are commonly referred to as showing "real", as distinct from "nominal", changes of GDP. GDP statistics are normally published quarterly and are "seasonally adjusted" to remove seasonal influences by applying factors based upon previous seasonal patterns.

The standard methods used for estimating GDP are described in a primer published by the United States Bureau of Economic Analysis

Limitations and adjustments

Household production

Among the economic activities that are not recorded in the national accounts is unpaid production within a country’s households. It has been estimated that for Britain such production amounts to over 40 per cent of GDP. That omission can in principle be corrected by constructing household accounts using surveys , to estimate the amount of time that householders devote to productive work. Several countries are planning to make household output estimates in that way and to publish them as addenda to their GDP statistics.

New technology

Another limitation of conventional measures of real GDP arises from the failure to make due allowance for the introduction of new technology. For example, the substitution of word-processors for typewriters produced what was really an output increase, but which may well have been treated as a price increase. The economist William Nordhaus has used a study of the changing methods of generating light to suggest that failure to allow for changes in technology had led to significant underestimates of real GDP growth as well as overestimates of inflation. , and it has been estimated that failure to take account of quality improvements had for long resulted in underestimates of real GDP growth in the United States of between 0.6 and 1.5 percentage points. . The effects of that failure can sometimes be mitigated by the use of "hedonic price indexes" (as described in the article on the price index) based upon studies of the different prices that people are willing to pay for available quality differences - as is becoming the practice in the United States for the treatment of some high-technology products.

Accuracy and reliability

The rate of change of GDP is a major factor affecting policy action to stabilise the economy (as noted in the article on macroeconomics). Errors in the GDP statistic can consequently be damaging, especially in view of the fact that a small error in its level can result in a large error in its growth. (The damaging Lawson boom in the Britain in the late 1980s was largely attributable to such an error ). Since it takes time for action in response to news of the GDP growth rate to take effect, the regulatory authorities and commercial organisations tend to react to early estimates which are often subject to substantial revision. (The average revision to Britain’s quarterly growth figures between 1961 and 2001 was 0.2 per cent as compared to an average growth rate of 0.6 per cent, but the error was much greater in the late 1970s when a 1.7 per cent year-to-year reduction in GDP was later revised to a rise of 2.7 per cent). Attempts have been made to assess the accuracy of the components of GDP statistics , but since GDP data is compiled from thousands of inputs, it is not possible to do a complete check. Some indication of its reliability is, however, possible by comparing GDP estimates that have been compiled in different ways. The United States GDP is calculated separately from incomes data and from production data, and the difference is termed the "statistical discrepancy" . Since the early 1990s that discrepancy has been substantial, with the real income measure growing faster than the real product measure. (In 1993 the statistical discrepancy peaked at 1% of GDP, and over 7 years the income measure grew at an average of 4.3% and the product side measure at 4.0%). Estimates of statistical discrepancies for other countries are available from an United Nations database

GDP comparisons

Exchange rates

In order to provide the information necessary for the preferred method of making international comparisons of GDP, a number of international organisations cooperate to provide "purchasing power parity" (PPP) exchange rates. A PPP exchange rate is defined by them as "the number of currency units required to buy goods equivalent to what can be bought with one unit of the currency of the base country, usually the US dollar". The method of calculation and the uses of PPP rates have been explained in an OECD statistics brief , and are set out in detail in an United Nations handbook Data on PPP rates are published by the OECD The alternative of using market exchange rates can produce grossly misleading comparisons. For example the OECD brief shows that (as percentages of the USA's GDP) it would overstate Japan’s 1999 GDP by almost 50 per cent and Switzerland’s by over 30 per cent, and give the false impression that both were higher than the USA’s

Accuracy and reliability

Comparisons using PPP exchange rates are in some cases still prone to substantial error. Developing countries do not all compile their national accounts in accordance with internationally accepted standards , their accounts will not take account of their subsistence farming outputs, and differences of custom, religion or taste may make inappropriate some items in the "basket" of purchased goods upon which the purchasing power parity rates are based.

Other indicators

It has been argued that the GDP should not be used as a policy target because it takes no account of matters of importance to the community, such as its health and the state of its environment, and there have been several attempts to convert it to a measure of the success of government policies. The Human Development Index (HDI) published by the United Nations adds such measures as literacy and life expectancy. The Index of Sustainable Economic Welfare (ISEW) published by Friends of the Earth, includes additions for welfare-producing services and deductions for pollution and environmental damage. The Genuine Progress Indicator (GPI) includes crime and income distribution, in addition to much of what is included in the ISEW. In all of such indicators, the choice of the factors to be included and of the relative weights to be attached to them are solely the result of the personal judgements of their creators.

See also

Francis Lequiller and Derek Blades Understanding National Accounts OECD 2006 [3]