The NBER is the USA's leading nonprofit economic research organization. Twelve of the 31 American Nobel Prize winners in Economics and three of the past Chairmen of the President's Council of Economic Advisers have been researchers at the NBER. The more than 600 professors of economics and business now teaching at universities around the country who are NBER researchers are the leading scholars in their fields. These Bureau associates concentrate on four types of empirical research: developing new statistical measurements, estimating quantitative models of economic behavior, assessing the effects of public policies on the U.S. economy, and projecting the effects of alternative policy proposals.