Time Charts 53

Horizontal bars drawn to a scale of time. Complex time charts by which the relations of numerous horizontal bars may be studied. Time charts showing bars combined with a curve expressing totals. Curves to study whether time schedules are maintained. Rank charts to portray the rank of different individuals at various times. Rank charts showing actual relative rank at any time and also changes in rank at various times. Traindispatching charts. Time-distance curves.

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GRAPHIC METHODS

Chapter V. Curve Plotting 69

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.

Chapter VI. Curve Plotting Continued 84

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. . .

Chapter VII. Comparison of Curves 107

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.