A METHOD OF GRAPHICAL ANALYSIS 



85 



that when the smoothing process is applied to one family, the effects 

 on the other may be more readily ascertained. 



The curves on Fig. 3A are the rough curves which were drawn 

 through the data on Fig. 2. Fig. 3B shows the cross sections of these 

 curves, message allowance being plotted and rank of service coded. 

 It is evident that neither set of curves is a consistent family. Most of 

 the curves of Fig. 3B are irregular instead of being smooth. They 

 might be smoothed considerably either by lowering the points cor- 

 responding to a 70 message allowance or by raising those for an al- 



CODE 



CROSS SECTIONS FROM FIG.3-A. 



CROSS SECTIONS REVISED 



DATA POINTS FOR 80-99 ALLOWANCE GROUP 



40 50 60 70 80 90 100 110 

 MONTHLY MESSAGE ALLOWANCE 



Fig. 3B 



lowance of 90 messages. A study of Fig. 3B shows that the curves 

 at 90 allowance are further apart than at any other point. This 

 might be used as an argument either for raising the lower points or 

 lowering the higher. In scrutinizing the data, however, it is found 

 that of the classes of service having from 80 to 99 allowance all have 

 allowances of either 80 or 83. Therefore, the midpoint (90 allow- 

 ance) is too high to represent the group, or, conversely, the message 

 use plotted is too low for an allowance of 90 messages. In order 

 to have a guide in the amount of shifting necessary, data points for 

 the actual message allowances of the 80-99 group have been plotted 



