THE CLASSES OF FREQUENCY POLYGONS. 21 



71 



^ 5 ~ 5"i4 + lOVva - lOVv., + 4y 1 5 ; 



(B) To find moments in case of graduated variates: 



y^ - 10V* 2 + 4y 1 5 - f /JA 5 ; 

 in which A is the class range expressed in the same unit as 

 the average. 



The probable error of the preceding constants in the special 

 case of the normal curve is as follows: 



Efi 2 = .67449<7 2 4/- ; E^= .67449 



71 ' 



= .6T4494 -; 



T 71 



= 67449 V // i <r ( p- 31) ; 



# of Skewness= .67449y 7^. (See page 30.) 

 (From Pearson, 1903 C ). 



The classification of any empirical frequency polygon 

 depends upon the value of its " critical function," F* (Pear- 

 son, 1901 d ). 



4(4A-3/? 1 )(2/? 2 -3A-6) < 



* This value of F is general. For the special case of Types I-IV 

 the following critical function was given by Pearson and has been 



