Comparison of Death Rates in the United States, Showing Reduction in Death Rate for Tuberculosis and Increase in Death Rate for Degenerative Diseases

This illustration is' identical with Fig. 246 except that here a wavy line is used at the base showing that the bottom of the chart is not at the zero of the vertical scale. It is always desu-able to have the bottom line at zero. If that is not possible the wavy line should be used as a warning to the reader

Though there is no necessity for showing Fig. 246 without having a zero line at the bottom of the chart. Fig. 248 is presented here to prove how easj^ it is to make a wavy line at the bottom of a chart if there should be any real reason why the chart cannot be made so as to include the zero hue of the vertical scale. Fig. 248 is exactly the same as Fig. 246 except that the wavy hue is used instead of the straight line at the bottom.

The beginner in curve plotting and in curve reading is apt to be somewhat puzzled by the different effects which may be obtained by changing the ratio between the vertical scale and the horizontal scale. It is difficult to give any general rules which would assist in overcoming the beginner's confusion. Ordinarily the best way to get facility in making the proper choice of vertical and horizontal scales for plot-

A FEW CAUTIONS 353

ting curves is to take one set of data and plot those data in several different ways, noticing the changes which the different scales selected give in the proportions of the chart. Just as the written or spoken English language may be used to make gross exaggerations, so charts and especially curves may convey exaggerations unless the person preparing the charts uses as much care as he would ordinarily use to avoid exaggeration if presenting his material by written or spoken words.