A better way to think about this is from the "Born On Third Base" report looking at the Forbes 400. In 2012, it was estimated only 35% of the wealthiest people grew up in low or middle class--as opposed to 95% of the general population.
Another way to say this is that 65% of the wealthiest people were born into the top 5%.
http://d3n8a8pro7vhmx.cloudfront.net/ufe/legacy_url/410/Born...