38 GENETICS IN RELATION TO AGRICULTURE 



(c) Mixing of distinct varieties, which must never be permitted if 

 known in advance. 



2. Definition of Population. The population must be so defined that 

 conclusions reached will not be wrongly applied to other populations. 



3. Typical Sample. The sample must be really typical of the species, 

 variety, breed, strain or race. Otherwise the results are not applicable to 

 large populations. Also the sample must be large enough so that con- 

 clusions may be drawn fairly. 



4. Sufficient Accuracy. Measurements must be made with a suf- 

 ficient degree of accuracy. It might be thought that a coarse or slightly 

 variable scale of measurement would satisfy since the measurements 

 are to be grouped, but the relative size of the groups is a most critical 

 matter so that the size of scale and degree of accuracy are very important. 

 Yet perfect accuracy is hardly obtainable. Relative not absolute ac- 

 curacy is the desideratum. As stated by King: For every statistical 

 problem there should be determined in advance a definite standard of 

 accuracy for each item and every endeavor should be made to bring each 

 recorded instance up to this standard. 



Grouping Variates into Classes. When the individuals have all been 

 measured the collection of variates must be grouped. The following 

 rules should be observed: 



1. Classes should be of equivalent ranges. One must not neglect 

 the extremely large and small variates. Employ a uniform scale through- 

 out all classes. 



2. Arrange the classes so there will be no possibility of mistake by the 

 reader. Calculations may be based on the centers of the class intervals 

 or on the upper limits of the intervals for certain purposes. 



The Frequency Table. A list of the classes formed by trie grouped 

 variates together with the number of individuals in each class is called a 

 frequency table. For example, Love and Leighty give the data on total 

 yield of plant in grams of Sixty Day oats for the year 1910 at Ithaca, 

 N. Y. These are presented in the form of a frequency table in Table II. 



TABLE II. FREQUENCY TABLE SHOWING VARIATIONS IN YIELD OP SIXTY DAY 

 OATS. (After Love and Leighty) 



(Class value = V (Frequency = /) ', (Class value = V) (Frequency /) 



.Grams of oats Number of plants Grams of oats Number of plants 



0-1 = 0.5 3 5-6 = 5.5 42 



1-2 = 1.5 50 6-7 = 6.5 7 



2-3 = 2.5 106 7-8 = 7.5 2 



3-^ = 3.5 109 8-9 = 8.5 1 



4-5 - 4.5 80 



Total number of individuals 400 = n 



