percentage of us population that have a phd
The 1.77% of US population is doctorate or equivalent degree holders (Educational attainment in the United States http://www.nsf.gov/statistics/in... ), that is roughly 5.6M. It is hard to find statistics about world PhD numbers due to lack of data availability. We can assume USA's doctorate population is skewed as its GDP number such as she has 4.4% population but 17% GDP of the world.