12 



STATISTICAL METHODS. 



This method of drawing the frequency polygon is known as 

 the method of rectangles. 



When the number of classes is large the frequencies may be 

 represented by ordinates as follows : At equal intervals along 



a horizontal line (axis of -X") draw a series of (vertical) ordi- 

 nates whose successive heights shall be proportional to the 

 frequency of the classes. Join the tops of the ordinates as 

 shown in Fig. 4. This method of drawing the frequency 

 polygon is known as the method of loaded ordinates. 



2600 LEAVES 



-NORMAL CURVE 



Q280 

 HI 



E 



NUMBER OF V!NS 

 FIG. 4. VEINS IN BEECH LEAVES, AFTER PEARSON, '02*'. 



The rejection of extreme variates in calculating 

 the constants of a distribution polygon is to be done only 

 rarely and with caution. In many physical measurements 

 Chauvenet's criterion is used to test the suspicion that a 

 single extreme variant should be rejected. A limiting devia- 

 tion (KG) is calculated. K is the argument in Table IV cor- 

 responding to a tabular entry equal to - 



