Principles of Graphical Display

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Principles of Graphical Display
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Tables and Graphs

• Meaningful data
• Unambiguous data
• Efficient display

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Meaningful Data

• Make Meaningful Comparisons
• Rates, ratios
• Before and after
• Cross sectional, between groups
• Time series
• Adjust for inflation

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Unambiguous

• Define data with titles, legends, labels,
  footnotes.
• Specify the source

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• Table 4 Change in Teenage Birth Rates 1987-1998
  White   6.7  Black -4.9  Asian
  -1.8 Hispanic   3.7 Source Statistical
  Abstract 2000, Table 85

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Efficient

• Minimize the ink-to-data ratio
• Sort data on meaningful variable (not
  alphabetical)
• Use consistent formatting across tables

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Ink to data ratio

• De-emphasize gridlines, borders and backgrounds
• Never use 3-D
• Display more than 1 variable
• Use data labels, not scales to minimize the
  number of numbers

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Proper sorting

• Time goes left to right
• Highlight comparisons

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Avoid Distortion

• Beware of scaling effects
• Use tables if variables are of different units
  e.g., dollars and percents.
• Adjust variables in common units to common
  starting point
• Use right and left scales

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Pies are badnote how the 3-D pie exaggerates the
relative size of the front slice
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2-D is better than 3-D, but..
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Bars provide a better visual image of relative
size than pie slices
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