This chart is grossly misleading because the point where the race started is not shown. It appears, for instance, that for one dollar expended a five-ton gasoline truck will run about twice as far as a five-ton horse truck. This conclusion is entirely unwarranted, and would not be reached by any reader if the chart had been so drawn that the zero point or starting point for the race had been shown to scale at the left end of the chart.

The black bars used in Fig. 30 to show contagious diseases indicate an excellent method for differentiating items shown in graphic comparison. In the Boston healthreport illustration from which this cut was adapted, the infectious diseases were shown in red. By making most of the bars in outline only, it was possible in Fig. 30 to use solid black to get the contrast obtained in the original report by means of red ink.

It is frequently necessary to show increases and decreases on the same chart so that they may

GRAPHIC METHODS

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^^ Defttht from InfectlouB Dlteaata. < I De&thB from other Olmgw,

^n«uaZ Report of the HeaUh Depanmcnr, City of Boston, 1910

Fig. 30. Comparative View of Twentyfive of the Principal Causes of Death in Boston During 191 o

In the Boston report, the infectious diseases were represented by red bars. Here attention is called to the infectious diseases by using solid black bars in contrast with bars shown only in outline

zero line. The figures can be placed on the left-hand margin of the chart, immediately between the title for each bar and the end of the bar, in a manner similar to that shown in Fig. 27. Since the zero line must be near the center of the chart, rather than at the left-hand edge, when the rightand-left arrangement is used, it