Goodwin A.
Ment Welf. 1928 Oct 15;9(4):81-85.
PMID: 28909218

FORD A.
J Appl Psychol. 1949 Aug;33(4):382-94. doi: 10.1037/h0062897.
PMID: 18135581

PADALINO F.
Rass Studi Psichiatr. 1950 Jul-Aug;39(4):493-525.
PMID: 14786499

NASH MC.
Am J Psychol. 1950 Apr;63(2):214-20.
PMID: 15410883

HOFFMAN PJ.
Psychol Bull. 1960 Mar;57:116-31. doi: 10.1037/h0047807.
PMID: 14402414

Brierley H.
Nature. 1967 Jun 03;214(5092):1056. doi: 10.1038/2141056a0.
PMID: 6055409

Burt C.
Ment Welf. 1939 Apr;20(2):45-48.
PMID: 28909160