CHAPTER 13. 



INFLUENCE OF CERTAIN PHYSICAL CONDITIONS ON THE INTELLIGENCE SCORE. 



Typhoid inoculation,. — Because of the criticisms frequently urged regarding the possible 

 injurious effects of a recent typhoid inoculation on performance in the psychological examina- 

 tion, a comparison was made at Camp Custer of the intelligence scores of 178 men who had 

 been given their complete inoculation approximately 24 hours before examination with the 

 scores of 239 men of the same unit who had not bad recent inoculation and also with the scores 

 of the entire increment of the same month, 7,167 men. 



The first comparison made was between 70 men, who themselves judged that their showing 

 on the scale had been affected by their recent inoculation, and the remaining 108 men, who felt 

 this to have had no effect. The means are practically identical. 



Typhoid inoculation. 



Men reporting effect from inoculation 



Men reporting no effect from inoculation . 



Number 

 of cases. 



70 

 108 



Mean 

 score. 



67.4 

 67.9 



Standard 

 deviation. 



33.5 



Comparing next the means of those recently inoculated with those not recently inoculated 

 wo have : 



Difference between means 6. 5 



Probable error of difference of the means 2. 29 



Ratio of the difference to probable error of difference 2. 84 



The difference found in the last comparison is of doubtful significance in view of the fact 

 that this group contained a good many superior men, who were being held over in the depot 

 brigade because of possible fitness for officers' training camps. The following comparison of 

 the inoculated group with the 7,167 men who made up the entire July, 1918, increment is deemed 

 more satisfactory: 



Difference between means 0. 6 



Probable error of difference of the means 1. 62 



Ratio of difference to probable error of difference 0. 37 



The results seem to show that no significant effect on alpha scores is produced by taking 

 the examination 20 to 24 hours after an antityphoid inoculation, and that the men's own judg- 

 ment on this point is unreliable. There are four chances in five that with another pair of 

 samples the difference would be reversed. 



Hookworm disease. — A comparison was made at Camp Travis between the intelligence scores 

 of 632 white men and 130 negroes who were infected with hookworm and the scores of 5,615 

 121435°— 21 52 809 



