Guttman, L. The Structure of Interrelations among Intelligence Tests. Proceedings of the 1964 Invitational Conference on Testing Problems, Princeton : Educational Testing Service, 1965 , 25-36.
2.
Mood, A. M. and F. A. Graybill : Introduction to the Theory of Statistics, McGraw-Hill, New York, 1963.
3.
Wilks, S. S.Mathematical Statistics, John Wiley, New York, 1962.