Cattell, R. B. "Extracting the Correct Number of Factors in Factor Analysis." EDUCATIONAL AND PSYCHOLOGICAL MEASUREMENT, XVIII (1958), 791-838.
2.
Guilford, J. P. and Lacey, J. I. "Printed Classification Tests." Vol. 5. Aviation Psychology Program Research Reports , U. S. Govt. Printing Office, 1947 .
3.
Humphreys, L. G. "The Organization of Human Abilities." American Psychologist, XVII (1962), 475-483.
4.
Kaiser, H. F. "The Application of Electronic Computers to Factor Analysis." EDUCATIONAL AND PSYCHOLOGICAL MEASUREMENT, XX (1960), 141-151.