Philip E. Converse, a professor emeritus in political science at the University of Michigan, is a seminal figure in the field of public opinion. His article "The Nature of Belief Systems in Mass Publics" (Ideology and Discontent, edited by David E. Apter, 1964) held that public opinion tended to be not very consistent across issues, not very stable over time, and not very understanding of ideology. With Angus Campbell , Warren Miller and Donald Stokes , he co-wrote The American Voter, an instrumental work of political science using data from National Election Studies, a set of important surveys of American public opinion carried out by the University of Michigan Survey Research Center and the Center for Political Studies.