274 The Dancing Mouse 



for the ten one-month individuals is 88 (that is, 88 tests were 

 necessary for the establishment of a habit) ; for the four-month 

 individuals it is 102.5. The heavy solid line of Figure 33 

 joins the points on the ordinates at which these values are 

 ) located. Apparently, then, the dancer acquires the white- 

 black discrimination habit less readily at the age of four 

 months than at the age of one month. 



Further analysis of the results proves that this statement 

 is not true. When the averages for the two sexes are com- 

 pared, it appears that the males learned much less quickly 

 at four months than at one month, whereas just the reverse 

 is true of the females. The dash and dot line of the figure 

 extends from the index of modifiability of the one-month 

 males (72) to that of the four-month males (120); and the 

 regularly interrupted line similarly joins the indices of the 

 one-month (104) and the four- month (85) females. In seek- 

 ing to discover age differences in docility or ability to profit 

 by experience we have stumbled upon what appears to be 

 an important sex difference. Perhaps I should add to this 

 presentation of partial results the following statement. Since 

 there are only four individuals in the four-month group, two 

 of each sex, the indices are not very reliable, and consequently 

 too much stress should not be laid upon the age and sex differ- 

 ences which are indicated. 



In view of this impressive instance of the way in which 

 averages may conceal facts and lead the observer to false 

 inferences, I wish to remark that my study of the dancer has 

 convinced me of the profound truth of the statement that 

 the biologist, whether he be psychologist, anthropologist, 

 physiologist, or morphologist, should work with the organic 

 individual and should first of all deal with his results as in- 

 dividual results. Averages have their place and value, but 

 to mass data before their individual significance has been 



