1. Francis Galton, Memories of My Life, Methuen. London, 1908, p. 302.
2. Cyril Burt, “Francis Galton and His Contributions to Psychology,” British Journal of Statistical Psychology, 13 (May 1962), 31.
3. Harold Hotelling, “Analysis of a Complex of Statistical Variables into Principal Components.” Journal of Educational Psychology. 24 (1933). 417–441 and 498–528.
4. Douglas F. Vincent, “The Origin and Development of Factor Analysis,” Applied Statistics, 2 (1953). 116.
5. Godfrey H. Thomson, The Factorial Analysis of Human Ability, 5th edn.. Houghton Mifflin. Boston. 1951. p. 94