1. von Bertalanffy, L. (1968).General system theory. New York: Braziller.
2. Buckley, W. (1967).Sociology and modern system theory. Englewood Cliffs, NJ: Prentice-Hall.
3. Coombs, C. H. (1964).Theory of data. New York: Wiley.
4. Coombs, C. H., & Kao, (1954).Nonmetric factor analysis. Ann Arbor: University of Michigan Engineering Research Institute.
5. Dahrendorf, R (1959).Class and class conflict in industrial society. Stanford: Stanford University.