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 the 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 I].—FREQquENCY TaBLE SHOWING VARIATIONS IN YIELD or Sixty Day 
Oats. (After Love and Leighty) 
=e = ° , = 7 
Sees eee Numt Hesear Meas et vom aie N ae Esa raison 
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 
3-4 = 3.5 109 8-9 =8.5 1 
4-5 = 4.5 80 
Total number of individuals................0.0. 400 = 
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