Page:Graphic methods for presenting facts (1914).djvu/187

 This allows the use of a large scale for the data of the upper floors. In order to see the general shape of a frequency curve when plotted with flat tops instead of peaked tops, the book may be turned so that the illustration is seen from the left-hand edge. This chart was drawn primarily as a wall exhibit, to be used later as an illustration in a printed report. The general scheme is excellent and it could scarcely be improved upon, even though the independent variable has here been made the vertical scale instead of the horizontal scale. Putting these data in the form of a curve such as is used in Fig. 143 would probably not be as effective for untrained readers as the black bars of Fig. 142, placed against a field in the general shape of a New York manufacturing building.

''Data of Amy Hewes, in Publications Am. Statistical Assn.''

Fig. 143. Age at Marriage of 439 Married Graduates of Mount Holyoke College who Graduated from 1890 to 1909

The vertical scale shows the percentage of the whole 439 who married at each age given on the horizontal scale. The totals of all percentage figures at the upper margin of the chart is 100 per cent. If a greater number of persons were included in a frequency curve of this sort the curve would be less irregular and the mode would show more distinctly

Fig. 143 shows a frequency diagram of the kind found most useful in ordinary work. The vertical scale here represents percentage, and the total of all the figures shown at the upper part of the chart added together is 100 per cent. Frequency curves are very often used, however, with numbers rather than percentages represented on the vertical scale, and the vertical scale then shows the actual number in each class. To assist the reader, the total number of observations made would usually be recorded, perhaps in the title of the illustration. In biological work observations are usually made in vast number, to permit making a very accurate conclusion regarding the general laws of frequency for any particular subject under consideration. For a great many problems of everyday life, however, the observations are not