Page:Graphic methods for presenting facts (1914).djvu/199

 words "more than", with an arrow, had been placed at the lower left-hand corner of the chart. In Fig. 155 a little study will show the advantages of plotting curves on a "more than" basis. The reader can see at a glance from this illustration that the wages for the western States are very much higher than the wages in the south Atlantic States. The position of the curves one above the other would lead the reader at once to think of the upper curves as showing higher wages. Here the upper curves do indicate the higher wages, but they would not do so if they were plotted on a "less than" basis instead of on a "more than" basis. Though it may cause some confusion at first, it seems desirable as a general rule that cumulative frequency curves should be plotted on a "more than" basis rather than on a "less than" basis.

Courtesy of W. S. Gifford, American Telephone & Telegraph Co.

Fig. 153. Answering Time of Different Classes of Operators in Telephone Work

Cumulative curves of this sort give information in much more condensed and clear form than possible with other methods of presentation. This particular chart is read on a "less than" basis, as can be seen by the general position of the curves as related to the scales. Notice that none of the calls is answered in less than two seconds