Heads of the BRICS countries (L to R) President Dilma Rousseff of Brazil, Russian President Dmitry Medvedev, Indian Prime Minister Manmohan Singh, Chinese President Hu Jintao and President Jacob Zuma of South Africa pose prior to the BRICS summit in New Delhi on March 29, 2012. - 

Before the economic crisis of 2008, many developing nations were growing by leaps-and-bounds, economically speaking, and their success seemed to signal a new age of emerging markets.

Fast forward to today and the picture has changed. Some countries were able to thrive through the past five years while others saw their wealth plummet.

“This is 40 percent of the global economy, 80 percent of the world’s population and there’s some very serious differences between these countries,"says Ruchir Sharma, head of emerging markets at Morgan Stanley. "and so we need to look at them on a much more individual basis rather than clump them all together."

Sharma is the author of a new book on the topic, “Breakout Nations: In Pursuit of the Next Economic Miracles.”

He says one way to understand the differences between these countries is by looking at "The Billionaire Index." When a country has a large number of billionaires compared to less wealthy citizens, “it shows there’s too much concentration of wealth at the top and that's likely to lead to resentment against the rich and wealth creation."

Another indicator? Watching what the locals are doing. “Before any big financial crisis, you’ll notice it’s really the locals that start to bolt first compared to the foreigners.”

Follow Kai Ryssdal at @kairyssdal