Page:Graphic methods for presenting facts (1914).djvu/189

 and the number of observations so limited that it is much better to use the straight-line method of Fig. 143 than to attempt to make a smooth curve. Sometimes a smooth curve may only mislead the reader, making the chart appear very accurate when in reality the data were so crude that only the roughest approximation is possible.

Fig. 145. Conjugal Condition of the Population of the United States in 1900 in Proportions of the Total Number of Each Age Group

Here the arrangement of Fig. 144 has been reversed so as to place age on the horizontal scale, since age is the independent variable. Having the data expressed in curves permits much clearer interpretation by the reader. Curves for male and for female may be instantly compared. The term "widowed" as applied to men was used to harmonize with the preceding illustration

Fig. 144 is copied from the Census Atlas for the 1900 Census. In the Atlas, colors were used for the different areas which must be represented here by cross-hatching. Though these illustrations hold some very valuable and interesting information, the information is contained in such manner that it is almost impossible for the reader to get it out. In the first place, age is the independent variable, but it has been made the vertical scale. The information sought is the percentage at different ages for each of the sexes, and this must be read from the horizontal scale, in violation of one of the most important rules for graphic work. Another bad feature of the chart is that data for male and female are shown in the right and left direction from the center line, making it almost impossible for the reader to compare the figures for male and female at any age under consideration. The data for the upper half of Fig. 144 are replotted in Fig. 145, and the reader would do well to