PSYCHOLOGICAL MEASUREMENTS. 



609 



observations on one evening and considering them as one group, is 

 partly a measure of astigmatism as well as of true variability. The 

 number of observations made at each axis was too small for satis- 

 factory determination of a separate mean or standard deviation. The 

 average mean variation, so-called, is found to be 8.7" for Squad A (see 

 lower right-hand corner of table 175). It is somewhat smaller in the 

 case of Squad B, being 5.3" for their normal measurements and 4.8" 

 for their low-diet averages. (See table 176.) 



Table 176. — Squad B — Visual efficiency and its mean variation. 

 [Values given in seconds on the arc of vision.] 



* Subject commonly wore glasses but not when tested. 



2 The right eye was used in the test as with the other subjects, but Mac informs us that he has 



better vision with his left eye. 

 ' Ham complained that his eyes were tired from reading on the train while coming to Boston. 



* This was the first session for Kim and this measurement was not given for lack of time. 



* Sue said he could see the fixation dot better in this test than in any previous experiment. 



In figure 115 the mean variations (see the two lower curves) are very 

 consistent from experiment to experiment, with a slight increase for 

 Squad B at the time of the first reduction date (January 13). The 

 curve for Squad A is definitely and consistently below that for Squad 

 B, with two sHght depressions on October 27 and November 24 and a 

 tendency to smaller variations near the close of the series of experi- 

 ments, but these fluctuations are certainly not larger than might 

 normally occur. 



The average thresholds for the two groups, as expressed in degrees 

 on the arc of vision and shown in the upper curves in figure 115, main- 

 tain from October 27 and November 17 about the same relative levels 



