26 STATISTICAL METHODS. 



a a = 18.0448 - 3.7965 = 14.2483. 



-,-i=%^ = s. 



^.sa-jytsi.^ 



_ 2000 (18.9846) 4/17.9846 g 171828 ' 0883( ' 556 ~ * 2643 ~~ * 0704) 



~~ 18.0448 y^ X 3.7840 X 14.2006 

 = 475.24, the number of cases in the modal class. 

 The equation of the theoretical curve is thus 



where x is the difference between the class magnitude and the mode, 

 regarding signs. 



Position of the mode, y Q = M - d = 3.501 - .523 ^ 2.978. 

 The mean percentage deviation of the theoretical ordinates from the 

 observed ordinates is 11.4* (Method A). This is calculated as follows: 



0.0 



6.1 40.7 

 + 23.2 11.1 



30.1 8.2 

 + 6.8 1.4 

 4- 8.4 2.0 

 + 4.9 1.8 



13.6 10.2 

 -f 6.1 8.5 



- 2.1 9.5 



+ 1.0 12.5 



+ 0.4 20.0 



MULTIMODAL CURVES. 



Multimodal curves are given when the frequency in the 

 different classes exhibits more than one mode. False multi- 

 modal curves result from too few observations, or when the 

 classes are made too numerous for the variates. By increas- 

 ing the number of variates or by making the classes more 

 inclusive some of the modes disappear. 



* The mean percentage deviation by Duncker's determination with 

 method B using the same data is 1.73# of area. 



