112 DOMESTICATED ANIMALS AND PLANTS 
VARIABILITY AS TO LENGTH OF EAR— STANDARD DEVIATION 
I Sf roa (Vem | 47a? 
5.0 I — 3.51 12.31 +1 12.31 
5-5 4 — 3.01 9.06 + 36.24 
6.0 6 — 2.51 6.30 + 37-80 
6.5 7 — 2.01 4.04 + 28.28 
7.0 19 — 1.51 2.28 + 43-32 
25 31 — LOI 1.02 + 31.62 
8.0 37 — 0.51 0.26 + 9.62 
8.5 59 — 0.01 0.00 
9.0 46 0.49 0.24 + 11.04 
9.5 39 0.99 0.98 + 38.22 
10.0 23 1.49 ea 51.06 
10.5 II 1.99 3-96 + 43-56 
11.0 2, 2.49 6.20 12.40 
11.5 I 2.99 8.94 8.94 
286 364.41 
Mean = 8.514. 364.41 + 286 = 1.2742. 
122) 
V 1.2742 = 1.13 — = standard deviation (c). 
This standard deviation is considered, therefore, as the uni- 
versal measure of variability, and the student will do well to 
work these values with original measurements until they come 
to have a real meaning. After this has been done for a time 
standard deviation will express as much about variability as does 
the radius about a circle. 
Coefficient of variability. But one further step is necessary 
in the mathematical study of variability. The mean length of 
ear in this case was 8.514 inches, and its variability, that is, its 
standard deviation, was 1.13 inches; the mean weight of ear 
was 8.807 ounces, and the standard deviation was 2.854 ounces. 
How now can we compare variability in inches with varia- 
bility in ounces? In other words, how can we tell whether 
this corn is more variable with respect to length than it is with 
respect to weight, or vice versa? We cannot tell by direct 
1 The plus sign denotes that decimals are dropped. 
