Again, this is a stupid statistic that inaccurately counts currently indebted but huge earning potential people (say, for example, a recent graduate of Harvard Business School) as "poorer" than a sub-Saharan subsistence farmer. Longer explanation here: http://blogs.reuters.com/felix-salmon/2014/04/04/stop-adding...
The statistic might be stupid, but it does a marvellous job of illustrating immense inequality in wealth distribution, something which is both factual and important. Would you not agree?
If the statistic is inaccurate then it does a bad job at illustrating the inequality, because it's falsity discredits the conversation. In fact, it would be detrimental to the goal of telling the inequality story.
Generally the reason statistics are so dangerous when used to support an argument is that the argument quickly becomes about the validity of the number rather than the underlying issue.
At a very basic level comparing wealth between economies requires all sorts of subjective normalisation which is pretty open to challenge, and accounting for things like student debt is obviously going to be contentious.
Frankly I consider it surprising that you can even find the calculation methodology for something like that.
The trouble is that a burger flipper will not make as much money as an inventor, programmer, or doctor, no matter how much time you spend demanding minimum wage increases. The former's job is far less effort-intensive than the others; even if you created a fascist state and ordered that all burger-flippers be paid as CEOs, you would immediately lose your CEOs as they all quit to become burger-flippers.
