PSYCHOLOGICAL MEASUREMENTS. 553 



of the reduced diet subjects. With the 63 college men of course the 

 eating was uncontrolled. Much of the apparatus used for the low-diet 

 research was likewise employed for the aviators. The laboratory- 

 conditions were perfectly comparable, and the procedure with the 

 measurements was nearly identical. These data will be referred to 

 from time to time for purposes of comparison, and will be designated as 

 ''normal series of 1917." 



Since at the most the normal data with Squad A are limited to those 

 obtained in one session, and therefore it will be necessary to refer to 

 other data in discussing the results with these men, it will be most 

 convenient to present the results for both squads simultaneously. 

 The data for any measurements will be tabulated for each squad 

 separately, but when plotted the same figure will commonly contain 

 curves for both squads. These curves may thus be compared directly 

 according to the number of the experiment for each squad. For exam- 

 ple, the data for the third experiment for each squad will be plotted on 

 the same ordinate but as Squad A had 10 sessions and Squad B only 8 

 the curve for the latter will be 2 points short. An effort has been made 

 to keep the tabular presentations and the figures uniform for all the 

 measurements so that the detailed descriptions will not have to be 

 repeated. 



Because of circumstances over which we had no control, there were 

 certain changes in the personnel of the two groups of men. This is 

 regrettable, particularly for the psychological measurements. Indi- 

 vidual variations in metabolism and allied physiological processes are 

 not so large as in these more complex functions, involving considerable 

 learning, with which we here have to deal. All things considered, 

 it must be counted as rare good fortune that the changes in personnel 

 were not more frequent, and, indeed, that it was possible to hold 

 together for so long a time 10 men in each of the two groups of 12. 

 Statistically, 10 men is not a very large group, but practically, and con- 

 sidering the complexity of the research, the sacrifices that it entailed 

 and its long duration, together with the unstable conditions in all 

 college-student bodies in 1917-18, it is remarkable that the study was 

 finished with so many of the original subjects still serving. A group 

 of 10 cooperative trustworthy subjects must, all things considered, 

 be regarded as an exceedingly satisfactory number on which to base 

 a result in such observations. Since this is the case, it has been 

 deemed best not to complicate the average results with the more 

 fragmentary records from those subjects who did not serve through- 

 out the period. It would be very difficult to equate the results for 

 individual differences when one subject dropped out and another came 

 into the group. Therefore, unless otherwise specified, the average for 

 any measurement with Squad A will be the average of the individual 

 results for the following ten subjects: Bro, Can, Gar, Gul, Mon, Moy, 



