118 DOMESTICATED ANIMALS AND PLANTS 
Advantages of statistical studies. From the standpoint of 
improvement, however, these methods give the breeder an 
opportunity to study characters carefully, to know their average 
value and the extent of their variability. Not only that, but 
records kept from year to year will show the breeder what 
progress, if any, he is making, and to what extent, if at all, the 
animal or plant is responding to his selection. 
Exercises. The student may well have much practice in solving distribu- 
tions for mean, standard deviation, and coefficient of variability. Eight 
actual distributions are appended, five in length and three in ounces, but 
the student should have practice in taking his own measurements and in 
making his own scheme and grouping. These different distributions arise 
from different varieties or from different conditions of growth. 
Length of ear Length of ear Weight of ear 
LC cian ed a f f J Pe Pol neh 
in in. 02. H 
Es I 3.0 I I 
3:0 3 = 35 a 5 4 3 
35 I 3] 40 I 5 3 si 9 8 
4.0 I 5 425 I I 6 af 16 Ti OY 
4.5 2 8 5.0 & 3 8 5 2 26 16 
5.0 7: 10 5-5 5 7 18 6 2 31 2 
5-5 Ir I4 6.0 8 ic 4t 7 38 40 28 
6.0 Ir 2 6.5 10 21 54 8 4i 39 ae 
6.5 2 33 | 70 | 15 33 73 9 35 37 39 
70 | 37 | S4 |] 75 | 2 56 | 65 | 10 | 2 32 36 
7:5 38 | 59 | 8.0 | 46 79 2/11 2 17 35 
8.0 638 47 8.5 $7 68 30 12 II 13 a2 
8.5 2 38 9.0 44 55 12 13 7 8 I4 
9.0 61 20 9.5 33 21 3 I4 2 3 7 
9.5 33 5 10.0 12 3 1 | 15 = || 4 
10.0 19 10.5 5 i 16 I 
10.5: 8 11.0 af 
11.5 I 
= 12,0) = =e 
397 | 327 258 362 308 | 264 , 27 | 280 
M= 8.015 M= 7.141 M= 8.322 M= 7.965 M= 7.063 M= 7.901 M= 7.860 M= 8.807 
o= 1.348 C= 1.267 O= 1.217 T= 1.018 T= 1.070 = 2.657 T= 2.502 T= 2.854 
C=16.82 C=17.74 C=14.62 C=12.78 C=15.15 C= 33.63 C=32.98 C= 32.41 
1" Principles of Breeding,” pp. 434, 435- 
