He is renowned for his application of systems theory to the study of political science. Policy analysts have utilized his five-fold scheme for studying the policy-making process: input, conversion, output, feedback and environment. Gunnell argues that since the 1950s the concept of "system" was the most important theoretical concept used by American political scientists. The idea appeared in sociology and other social sciences but it was Easton who specified how it could be best applied to behavioral research on politics