Graphic Methods for Presenting Facts
The increase in deatti rates for ages over forty is here showTi in great contrast with the decrease in death rates for ages less than forty. The hea^"^' zero line and the arrows pointing upward and downward make misinterpretation almost impossible
It would have been better if Fig. 151 had, at the lower left-hand corner, the words "more than", with an arrow pointing horizontally to the right as can be seen in Fig. 158. In cumulative frequency curves
GRAPHIC METHODS
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such as this it is well to give the reader a clew that it is a cumulative frequency curve he is observing, and the arrow with the words more than" accomplishes this result in a satisfactory manner.
There are two scales used in Fig. 151 with the expectation that the reader would ordinarily use the left-hand scale when reading the chart,
using the words "more than". The right-hand scale reading downward permits the reader to get at once the complement of any figure on the left-hand scale, so that, by using the right-hand scale, the reader may interpret the curves on a "less than" basis. Thus, in considering the weight, roughly 6 per cent of all the rails on the system are more than 75 pounds per yard, and using the right-hand scale it is seen that, roughly, 94 per cent of all the rails are "less than" 75 pounds per yard. There is not ordinarily any necessity for using a double scale in this manner. It is done here only to show the difference in reading a two-scale chart. In Fig. 152 and also in Fig. 153 the cumulative curves have been plotted on a different basis from that used in plotting Fig. 150 and Fig. 151.