The United States of Inequality - In 1915, a statistician at the University of Wisconsin named Willford I. King published The Wealth and Income of the People of the United States, the most comprehensive study of its kind to date. The United States was displacing Great Britain as the world's wealthiest nation, but detailed information about its economy was not yet readily available; the federal government wouldn't start collecting such data in any systematic way until the 1930s. One of King's purposes was to reassure the public that all Americans were sharing in the country's newfound wealth. King was somewhat troubled to find that the richest 1 percent possessed about 15 percent of the nation's income. (A more authoritative subsequent calculation puts the figure slightly higher, at about 18 percent.)

http://www.slate.com/articles/news_and_politics/the_great_divergence/features/2010/the_united_states_of_inequality/introducing_the_great_divergence.html