50 Plant-Breeding 



/ = F*IOO. 



Probable error. 1 It is obvious that these mathematical 

 expressions of type and variability will be modified some- 

 what by the number of individuals measured. The 

 greater the number of individuals employed, the less the 

 error. These differences which arise from the fewness 

 of individuals employed is known as the probable error. 

 It is expressed by a pair of divergences (=t E), the one 

 above and the other below the actual value found, and 

 indicates that the chances are even that the true value 

 lies somewhere between the value found plus the error 

 and the value minus the error. .For example, the probable 

 error of the mean in the problem here cited is == .016 and 

 is found by the formula given below. This means that 



1 Formulae for probable errors : 



E mean = .6745 standard deviation 



number of individuals 



E standard deviation = * .6745 standard deviation - _ 



V2 X number of individuals 



E coefficient of variability = .6745 coefficient of variability 



v 2 X number of individuals 



C 



= .6745 7= 

 V2n 



But when C is greater than 10% use the formula 



