Page:Graphic methods for presenting facts (1914).djvu/130

Iron Age

Fig. 99. Price of 6-Inch Cast-Iron Water Pipe per Net Ton in Carload Lots at New York City, Compared with Price of Gray Forge Pig Iron per Gross Ton at Philadelphia

Notice how closely the price of cast-iron pipe depends upon the price of the material used in making it. There is not great variation in the margin between cost of material and cost of product

The chart greatly exaggerates the fluctuation in the price of pig iron. The rapid reader is not apt to notice that the scale of prices begins at $11 per ton and not at zero. If the chart were so made as to show the zero line it would give a different impression. Dates are better shown at the base of a chart than at the top

There is probably a fallacy in Fig. 100 because of the rise in the general standard of living between 1901 and 1906. It is not fair to the 1901 Princeton men to expect that they would earn as much immediately after graduation as men who graduated in a period of time several years later. In addition to this there is probably another serious fallacy which affects all three curves shown on the chart. The income figures from which the curves are plotted may not all be shown on the same basis. Men working on a salary have as net cash all the money they receive. Men in professions such as law, medicine, etc., where office rent and other expenses are likely to be very heavy, may report, as earnings, the total amount of money received without making corrections for the expenses of conducting their business. In other words, they may very possibly in this case report gross income instead of net income. Such procedure might tend to make the curves for average income considerably higher than they would otherwise be.

Complex charts made up of groups of bars as seen in Fig. 101 are much more common than they should be. This type of chart is very annoying to