PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 4 OCTOBER 15, 1918 Number 10 
MEASURING THE MENTAL STRENGTH OF AN ARMY 
By Major Robert M. Yerkes 
Sanitary Corps, N. A. 
Communicated by R. Pearl. Read before the Academy, April 23, 1918 
Committees of the American Psychological Association and the Psychology 
Committee of the National Research Council prepared between April and 
August, 1917, various psychological methods for the selection and classifica- 
tion of recruits in the Army and Navy. In August, 1917, the Surgeon General 
on recommendation of Majors Victor C. Vaughan and William H. Welch of the 
National Research Council accepted for trial certain methods which had been 
devised especially for the psychological examination of men enlisted in the 
United States Army. Dr. Robert M. Yerkes, Chairman of the Psychology 
Committee of the National Research Council was appointed on August 17, 
Major in the Sanitary Corps, to organize and direct this new branch of the 
service for the Medical Department. 
During the initial development of this service, Major Yerkes worked under 
the immediate administrative supervision of Major Pearce Bailey, Chief of 
the Division of Neurology, Psychiatry and Psychology. Plans were speedily 
prepared and the necessary authorization secured from the Secretary of War 
for thorough trial of the proposed methods in four National Army canton- 
ments. For this work sixteen psychologists were commissioned first lieuten- 
ants in the Sanitary Corps, and twenty-four others were given civil appoint- 
ment by special authorization of the Secretary of War. The psychological 
staff of each camp consisted of ten men. 
Between October 1 and December 1, 1917, nearly 100,000 drafted men, 
students in Officers' Training Camps, and officers of camps or divisions were 
examined. In December the work was officially inspected by an officer of 
the Medical Corps. The reports of this inspectional officer supplemented im- 
portantly the statistical data supplied during progress of work by Major Yerkes. 
As the results of psychological examining indicated clearly the value of the 
work for the elimination of men mentally defective, the balancing of organi- 
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