80 MODES OF RESEARCH IN GENETICS 



Such a count furnishes us at once with a great 

 deal of perfectly definite and precise information 

 about this group or population of balls. For 

 example, the count tells us that it will never be 

 possible to draw more than one pair of balls of 

 which one member is green. This is a definite 

 attribute of this population which may be used to 

 differ entiate it from other populations. In this 

 particular population only one green ball occurs. 



This sort of knowledge derived by counting is 

 perfectly definite and precise so far as relates to the 

 particular group or mass which it concerns in 

 any particular case. It does not involve any 

 approximation, or probability, and is as precise 

 as knowledge of the individual. It, however, 

 pertains to the group. It forms a part of a proper 

 scientific description of a group. 



2. Knowledge of certain abstract qualities of 

 groups or masses. This knowledge is obtained by 

 calculation from the counted data. The more 

 important of the abstract qualities of groups are : 



a. The center or typical condition of the group ; 

 or the condition about which the individuals 

 composing the group cluster. This is variously 

 measured : by the arithmetic mean, which gives 

 the center of gravity of the group, by the median, 

 which tells the point on either side of which 

 exactly half the individuals fall, by the mode, 

 which tells the point of greatest frequency of 

 occurrence in the group, etc. 



