Developed by Norwegian mathematician MARIUS SPOHUS LIE (1842-1899) and later adopted by modern economists, group theory is a method of analyzing invariant relationships among economic variables where often the relationships are represented by differential equation systems.
R Sato, Theory of Technical Change and Economic Invariance: Application of Lie Groups (New York, 1981)
Discipline: Political Science
Theory developed in the USA, of politics as the action of groups.
Neither individuals nor whole societies are significant political actors. The actions of groups in pursuit of their various interests are the sources of policy and the substance of politics.
Group theory is thus a species of pluralism.
Bernard Crick, The American Science of Politics (Berkeley, 1959)