Gross Domestic Product - Cross-border Comparison and PPP

Cross-border Comparison and PPP

The level of GDP in different countries may be compared by converting their value in national currency according to either the current currency exchange rate, or the purchase power parity exchange rate.

• Current currency exchange rate is the exchange rate in the international currency market.
• Purchasing power parity exchange rate is the exchange rate based on the purchasing power parity (PPP) of a currency relative to a selected standard (usually the United States dollar). This is a comparative (and theoretical) exchange rate, the only way to directly realize this rate is to sell an entire CPI basket in one country, convert the cash at the currency market rate & then rebuy that same basket of goods in the other country (with the converted cash). Going from country to country, the distribution of prices within the basket will vary; typically, non-tradable purchases will consume a greater proportion of the basket's total cost in the higher GDP country, per the Balassa-Samuelson effect.

The ranking of countries may differ significantly based on which method is used.

• The current exchange rate method converts the value of goods and services using global currency exchange rates. The method can offer better indications of a country's international purchasing power and relative economic strength. For instance, if 10% of GDP is being spent on buying hi-tech foreign arms, the number of weapons purchased is entirely governed by current exchange rates, since arms are a traded product bought on the international market. There is no meaningful 'local' price distinct from the international price for high technology goods.
• The purchasing power parity method accounts for the relative effective domestic purchasing power of the average producer or consumer within an economy. The method can provide a better indicator of the living standards of less developed countries, because it compensates for the weakness of local currencies in the international markets. For example, India ranks 10th by nominal GDP, but 3rd by PPP. The PPP method of GDP conversion is more relevant to non-traded goods and services.

There is a clear pattern of the purchasing power parity method decreasing the disparity in GDP between high and low income (GDP) countries, as compared to the current exchange rate method. This finding is called the Penn effect.

For more information, see Measures of national income and output.