Global Price Indexes
The World Price Index is calculated monthly from a basket of internationally comparable goods and services. It is designed to alleviate the horrendous problems associated with analysing economic or market data using currency market exchange rates.
To illustrate the problem:
"Imagine that over the last 4 years the US economy has shrunk by 30% and the Chinese economy grown at 2% not 10%. Imagine house prices in the UK have dropped 60% ...This frozen wasteland is not some alternative universe , but what reality already looks like when expressed...in the Japanese Yen"
(quoted from an FT article by Peter Tasker in 2011)
Exchange rates vary with extraordinary rapidity, frequently with little obvious link to economic reality, but fatally distorting the perception of value in markets and economies. It is vital when analysing international data, whether for market analysis purposes, or to allocate resources across the globe, to review data using an international yardstick of value. This can only be done using Puchasing Power Parities (PPP), which make allowance for the purchasing power of currencies within individual countries to make comparisons based on a standard currency, usually "international dollars".
There are various sources of PPP data, but most are of only academic interest as they are years out of date. The World Price Index is the only available index updated monthly to provide an easy way of reviewing trends or relative values of market or economic data in realistic terms.