Page:Graphic methods for presenting facts (1914).djvu/161

 The lower half of Fig. 127 contains three curves showing the monthly distribution, for three successive years, of about 700 deaths annually from industrial accidents reported from an area embracing 80,000 plants. The similarity of these curves, showing the number of fatal accidents per month, to the curves showing the percentage of darkness, is intended to convey to the person seeing the wall exhibit, the truth of the statement at the top of the chart, that "an abundance of light tends to prevent industrial accidents." Though Fig. 127 is a very commendable and effective piece of work, it should be pointed out that there is danger of exaggerating the facts in the way in which the chart is prepared. The lower left-hand scale does not begin at zero. By measuring, it can be seen that the scale begins at 20 accidents per month. The bottom line of the curve field should have been drawn near the edge of the picture frame to represent zero. This change in the bottom line would have given the reader a more accurate idea of the increase of deaths in those months having the greatest proportion of darkness. This chart really does not exaggerate the facts seriously, for the three curves for deaths and the curve for darkness would really be of approximately the same shape even if the zero line had been shown in its correct position. Yet it is a fact that the omission of the full scale in the chart may cause a person glancing hastily at the chart to distrust it simply because the zero line is not shown.

In Fig. 128 a number of different components are shown to make up a total of 100 per cent. This type of chart is especially good to give instantly a general idea of the relative size of the components or factors which enter into any total, and to show the changes in these factors as time goes on. Though it is fairly easy to see in Fig. 128 what the changes are which have occurred in, say, the item for "General" expenses, it is not at all easy to determine the changes which have occurred in the item for "Conducting Transportation." The eye cannot measure correctly the increase or decrease in width of any area as great as that representing the item for "Conducting Transportation," especially if there is no straight line to gauge by, either at the top or the bottom of the area under consideration.

Though the method of presenting the facts in Fig. 128 is excellent to give a rough general idea or to reach unskilled readers, the method of presenting the facts in Fig. 129 is likely to give the more accurate impression. In Fig. 129, each of the different expense accounts is