# Difference between revisions of "Purchasing power parity"

Purchasing Power Parity (PPP) of Gross Domestic Product for the countries of the world as of 2003. The economy of the United States is used as a reference, so that country is set at 100. Bermuda has the highest index value, 154, thus goods sold in Bermuda are 54% more expensive than in the United States.

Purchasing power parity (PPP) is an alternative measure of the wealth of nations based on the long-term equilibrium exchange rate of two currencies to equalize their purchasing power. Developed by Gustav Cassel in 1918,[1] it is based on the law of one price: the theory states that, in ideally efficient markets, identical goods should have only one price.

This purchasing power SEM rate equalizes the purchasing power of different currencies in their home countries for a given basket of goods. Using a PPP basis is arguably more useful when comparing differences in living standards on the whole between nations because PPP takes into account the relative cost of living and the inflation rates of different countries, rather than just a nominal gross domestic product (GDP) comparison. The best-known and most-used purchasing power parity exchange rate is the Geary-Khamis dollar (the "international dollar").

PPP exchange rate (the "real exchange rate") fluctuations are mostly due to market exchange rate movements. Aside from this volatility, consistent deviations of the market and PPP exchange rates are observed, for example (market exchange rate) prices of non-traded goods and services are usually lower where incomes are lower. (A U.S. dollar exchanged and spent in India will buy more haircuts than a dollar spent in the United States). PPP takes into account this lower cost of living and adjusts for it as though all income was spent locally. In other words, PPP is the amount of a certain basket of basic goods which can be bought in the given country with the money it produces.

There can be marked differences between PPP and market exchange rates. [2] For example, the World Bank's World Development Indicators 2005 estimated that in 2003, one United States dollar was equivalent to about 1.8 Chinese yuan by purchasing power parity [3] — considerably different from the nominal exchange rate that put one dollar equal to 7.6 yuan. This discrepancy has large implications; for instance, GDP per capita in the People's Republic of China is about US$1,800 while on a PPP basis it is about US$7,204. This is frequently used to assert that China is the world's second-largest economy, but such a calculation would only be valid under the PPP theory. At the other extreme, Japan's nominal GDP per capita is around US$37,600, but its PPP figure is only US$30,615.

## Explanation

Let $P be the value in dollars of a representative basket of goods, and £P the value in pounds sterling of the same basket. We call$P/£P the PPP exchange rate.

If the actual spot rate is greater, it suggests that the pound is over-valued against the dollar. If the actual spot rate is less, it suggests that the dollar is over-valued against the pound.

## Need for PPP adjustments to GDP

Gross domestic product (by purchasing power parity) in 2006

Using market exchange rates to compare countries' standard of living or per capita Gross Domestic Product can give a very misleading picture. The exchange rate only reflects traded goods in contrast to non-traded ones. Also, currencies are traded for purposes other than trade in goods and services, e.g., to buy capital assets whose prices vary more than those of physical goods. Also, different interest rates, speculation, hedging or interventions by central banks can influence the foreign-exchange market.

The PPP method is used as an alternative.

For example, if the value of the Mexican peso falls by half compared to the U.S. dollar, the Mexican Gross Domestic Product measured in dollars will also halve. However, this exchange rate results from international trade and financial markets. It does not necessarily mean that Mexicans are poorer by a half; if incomes and prices measured in pesos stay the same, they will be no worse off assuming that imported goods are not essential to the quality of life of individuals. Measuring income in different countries using PPP exchange rates helps to avoid this problem.

PPP exchange rates are especially useful when official exchange rates are artificially manipulated by governments. Countries with strong government control of the economy sometimes enforce official exchange rates that make their own currency artificially strong. By contrast, the currency's black market exchange rate is artificially weak. In such cases a PPP exchange rate is likely the most realistic basis for economic comparison.

## Difficulties

The main reasons why different measures do not perfectly reflect standards of living are

• PPP numbers can vary with the specific basket of goods used, making it a rough estimate.
• Differences in quality of goods are hard to measure and thereby reflect in PPP.

PPP calculations are often used to measure poverty rates. For problems with this methodology, see How Not To Count The Poor.

### Range and quality of goods

The goods that the currency has the "power" to purchase are a basket of goods of different types:

1. Local, non-tradable goods and services (like electric power) that are produced and sold domestically.
2. Tradable goods such as non-perishable commodities that can be sold on the international market (e.g. diamonds).

The more a product falls into category 1 the further its price will be from the currency exchange rate. (Moving towards the PPP exchange rate.) Conversely, category 2 products tend to trade close to the currency exchange rate. (For more details of why, see: Penn effect).

PPP calculations tend to overemphasise the primary sectoral contribution and underemphasise the industrial and service sectoral contributions to the economy of a nation.

### Difficulties with PPP comparisons in welfare economics

While using PPP exchange rates for income comparison is an improvement over using market exchange rates, it is still imperfect, and comparisons using the PPP method can still be misleading. Comparing standards of living using the PPP method implicitly assumes that the real value placed on goods is the same in different countries. In reality, what is considered a luxury in one culture could be considered a necessity in another. The PPP method does not account for this. (This is not primarily a flaw in the exchange rate methodology, as cultural and interpersonal differences in utility functions are a more fundamental microeconomic problem.)

A PPP exchange rate varies depending on the choice of goods used for the index (CPI). Hence, it is possible to deliberately or accidentally bias a PPP exchange rate by the choice of a bundle. Indeed, it may be hard to construct equivalent representative bundles for the consumption habits of very different societies. PPP could also have difficulty accounting for differences in quality between goods in one country and equivalent goods in another, see: consumer price index.

## Clarification to PPP Numbers of the IMF

The GDP number for all reporting areas are one number in the reporting areas local currency. Therefore, in the local currency the PPP and market (or government) exchange rate is always 1.0 to its own currency, so the PPP and market exchange rate GDP number is always per definition the same for any duration of time, anytime, in that area's currency. The only time the PPP exchange rate and the market exchange rate can differ is when the GDP number is converted into another currency.

Only because of different base numbers (because of for example "current" or "constant" prices, or an annualized or averaged number) are the USD to USD PPP exchange rate not 1.0, see the IMF data here: [1]. The PPP exchange rate is 1.023 from 1980 to 2002, and the "constant" and "current" price is the same in 2000, because that's the base year for the "constant" (inflation adjusted) currency.