Page:Graphic methods for presenting facts (1914).djvu/16

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The desirability of using only well-known methods of presentation. Curves permit a more rapid and more accurate interpretation than possible by other methods. Studies of the causes of crests and valleys of curves. Curves especially needed for complex data. The use of curves in advertising. Polar co-ordinates objectionable for presenting statistical data. Examples of good practice in curve plotting.

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Independent and dependent variables. Confusion caused if the independent variable is not used for the horizontal scale. Examples showing correct arrangement of scales. Curves to advertise newspaper circulation. Curve charts combining much complex information. The use of two sets of co-ordinate ruling for the vertical scale. Moving averages. Smoothing curves. Index numbers. Weighted averages. Curve studies of national prosperity.

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Similarity and contrast of curves plotted in the same field. The zero of the vertical scale should be shown on the chart. Advantages of plotting curves for different years one above the other for comparison. Contrast in shape of curves plotted in separate fields. Advantage from shading the space under a curve. Numerous dissimilar but related curves on the same sheet. Errors resulting if curves not having the same zero line are compared. A total curve plotted from several other curves. Inverse relations, one curve trending downward when another trends upward. Study of correlation by plotting a curve from the data of two other curves. The angle of a curve on ordinary rectangular co-ordinates tells nothing about the percentage rate of growth. Disadvantages of the arithmetical scale ruling for curve plotting. Advantages obtained by plotting curves on logarithmically ruled paper.

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Use of vertical bars with components totalling 100 per cent. Shaded area under a curve when the height of the total field represents 100 per cent. The use of several areas in a curve field which totals 100 per cent. in height. A contrasting method of showing all curves plotted separately but from the same zero line. Universal co-ordinate paper for convenience in curve plotting. Total curves with component areas so that any point on a curve totals 100 per cent for the height of the areas beneath.

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Factory production schedules and actual outputs plotted on a cumulative basis. Curves for income and expense on a cumulative basis. Various uses for cumulative curves. Cumulative curves with lines drawn to show rate