The PPP exchange-rate calculation is controversial because of the difficulties of finding comparable baskets of goods to compare purchasing power across countries.

Estimation of purchasing power parity is complicated by the fact that countries do not simply differ in a uniform price level; rather, the difference in food prices may be greater than the difference in housing prices, while also less than the difference in entertainment prices. People in different countries typically consume different baskets of goods. It is necessary to compare the cost of baskets of goods and services using a price index. This is a difficult task because purchasing patterns and even the goods available to purchase differ across countries. Thus, it is necessary to make adjustments for differences in the quality of goods and services. Additional statistical difficulties arise with multilateral comparisons when (as is usually the case) more than two countries are to be compared

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