The following curve represents the variations in the length 

 of 448 seeds of bean (DeVries) : — 



It will be noted 

 that the curve is a 

 normal curve sym- 

 metrically developed 

 on both sides. Such 

 a curve of variabil- 

 ity expresses the fact 

 that a large propor- 

 tion of the beans are 

 near the average 

 length of 11 to 13 

 mm., those differing 

 from this being rela- 

 tively few on either 

 side of the average. 

 The mode of the 

 curve is 12 or the 

 group containing the 

 largest number of in- 

 dividuals of a kind. 

 The following table represents the variability of milk 

 production of 1,200 cows (Davenport): 



Len^tn 



Fig. 3. — Frequency of Curve of the Varia- 

 tions In Length of 448 Seeds of Beans. 



The curve would show clearly that the majority of the 

 cows yield between 4,500 and 6,500 lbs. of milk per year. 



The average length of the beans is ascertained to be 

 12 mm., and the average milk production 5.515 lbs. 



Deviation. — The variability, or deviation from the 

 average, gives us information as to the range of the devia- 

 tion. There are two methods of measuring this deviation, 

 the Average Deviation and the Standard Deviation. The 

 average deviation of the beans is calculated as follows (12 

 being average length) : 



1 (12-8) + 2 (12-9) + 23 (12-10) + 108 (12-11) + 

 167 (12-12) + 106 (13-12) -|- 33 (14-12) + 7 (15-12) 

 -f 1 (16-1 2) -^ 448; which gives .8mm. 



25 



