Page:Graphic methods for presenting facts (1914).djvu/147

 curves in the second chart should be the same as those for the first chart, so that there may be no "faking" in any similarity which may show up in the shapes of the two curves. It frequently happens that the relations between two curves are such that the most striking presentation can be obtained by plotting one curve upside down so as to bring the two curves as closely into coincidence as possible, and the scheme should be kept in mind as it is frequently of assistance in making facts stand out vividly.

Courtesy of Pennsylvania Farmer

Fig. 117. Exports of Apples from the United States as Compared with the Average Wholesale Price in the United States

A little inspection shows that the export curve usually goes up when the price curve comes down. Though this fact indicates an inverse relation between the two curves under consideration it does not give satisfactory proof that exports fluctuate relatively as much as price.

This chart is likely to mislead the reader because the two vertical scales do not have the same zero line. Curves compared in this manner without having a common zero line should always be distrusted

Another interesting study can be made from Fig. 117 by drawing a chart with "Price" as the horizontal scale and quantity of "Exports" as the vertical scale. Dots for the different years placed on such a chart, after the general manner of Fig. 119, will appear so widely scattered over the whole field that the reader will find it almost hopeless to draw any general conclusion from the arrangement of the dots. Though the dots indicate by their position a general tendency