Page:Graphic methods for presenting facts (1914).djvu/198

 two charts cannot be gone into here, but the reader can see for himself the use of the cumulative frequency curve in studying different problems in the telephone business. In Fig. 152 the curves show the time required to answer calls in different cities, while Fig. 153 shows a comparison of answering times in different classes of service. Notice that in each of these two charts it seems that two seconds is about the minimum which can be expected in answering telephone calls with the existing types of equipment. Fig. 153 certainly gives in excellent manner the comparison between the answering times for different classes of service. It would be very difficult to convey the complex information contained in Fig. 153 by using tabulated figures only. Tabulated figures would take up as much space as the chart and they would be less intelligible to any person who knows even the rudiments of reading graphic presentations.

Courtesy of Data, Chicago

Fig. 152. Time Required for Operators to Answer Telephone Calls in Towns of Different Size in Wisconsin

These curves start at the lower left-hand portion of the field and trend upward, showing that they are plotted on a "less than" basis. Curve A shows a smaller time required to answer calls than Curves B or C, yet the actual position of Curve A on the chart is higher than either curves B or C. If cumulative frequency curves are plotted on a "more than" basis the position of several curves on a chart is relatively such that the reader is not confused so much as when curves are plotted on a "less than" basis

In Fig. 154 an attempt was made to apply cumulative frequency curves to a comparison of wage rates in different sections of the United States. The chart, however, is likely to be very misleading, as it has been plotted by methods which are not in accordance with usual practice. The variables have been reversed, and the independent variable has incorrectly been made the vertical scale. Besides that, the vertical scale reads downward instead of upward. In all kinds of curve plotting it is common to have the two scales begin with zero at the lower left-hand corner of the chart. Here the two scales begin the zeros at the upper left-hand corner of the chart. Unless the reader will turn Fig. 154 on its side so as to make the two zeros at the lower left-hand corner, he may find great difficulty in interpreting the chart.

Fig. 155 shows a replot of the data of Fig. 154. Here the curves are plotted on a "more than" basis, but it would have been better if the