Statistics

Although less popularly known for these advances, Friedman was also widely agreed to be a brilliant statistician. Friedman did statistical work at the Division of War Research at Columbia. He and his colleagues came up with a sampling technique, known as sequential sampling, which became, in the words of The New Palgrave Dictionary of Economics: “The standard analysis of quality control inspection.”
The dictionary adds: “Like many of Friedman’s contributions, in retrospect it seems remarkably simple and obvious to apply basic economic ideas to quality control; that however is a measure of his genius.”

Source: http://www.econlib.org/library/Enc/bios/Friedman.html

Su-Min Yuen