Why is per-capita income NOT always the best indicator of an emerging market's potential? What does the concept of purchasing power parity (PPP) suggest?

What will be an ideal response?

When evaluating the potential of individual markets, managers often start by examining aggregate country data, such as gross national income (GNI) or per-capita GDP, expressed in terms of a reference currency such as the U.S. dollar. However, per-capita GDP converted at market exchange rates paints an inaccurate picture of market potential because it overlooks the substantial price differences between advanced economies and emerging markets. Prices are usually lower for most products and services in emerging markets.
Economists estimate real buying power by calculating GDP statistics based on purchasing power parity (PPP). The PPP concept suggests that, in the long run, exchange rates should move toward levels that would equalize the prices of an identical basket of goods and services in any two countries. Since prices vary greatly among countries, economists adjust ordinary GDP figures for differences in purchasing power. Adjusted per-capita GDP more accurately represents the amount of products consumers can buy in a given country, using their own currency and consistent with their own standard of living.