Displaying Data

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Displaying Data

• in Graphs and charts

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Challenger Disaster
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Report of the Presidential Commission on the
Space Shuttle Challenger Accident, 1986 (vol 1,
p. 145)
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How to Display Data (Badly)

• Showing the data (choosing the data)
• Showing data accurately
• Showing data clearly

H Wainer(1984). How to display data badly.
American Statistician 38(2)137-147. http//www.js
tor.org/view/00031305/di020581/02p0048x/0
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Showing Data
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Showing data

• Edward Tufte
• Data Density Index
• Chart Junk
• It does not make sense to use graphs to display
  very small amounts of data.
• The human brain is quite capable of grasping up
  to three values.

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Showing Data
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Showing Data

• Graphs are only as good as the data they display.
• No amount of creativity can produce a good graph
  from dubious data.

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Showing Data
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Showing Data Accurately

• Graphs should not provide a distorted picture of
  the values they portray.
• Distortion can be either deliberate or
  accidental.
• Common Distortions
• Use of 3 dimensional effects
• Use of linear scaling when using area or volume
  to represent values.

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3 dimensional effects
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No 3D Effect
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Linear Distortion
Fact 1973 dollar 0.44 1958 dollar 1
Dimensions 1958 dollar is less than twice the
height and width of the 1973 dollar
Area 1958 dollar has 3x the area
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No Distortion
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Hiding Information
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Not so hidden
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Showing Data Clearly

• Graphs should be no more complex than the data
  which they portray
• Unnecessary complexity can be introduced by
  chartjunk
• irrelevant decoration
• color

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Showing Data Clearly

• Age Structure of College
• Enrolment (1972-1976)
• 4 variables
• 6 colors
• Weird perspective
• SPLIT AXIS
• American Education Magazine.

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Showing Data Clearly
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Tips for Good Graphs, Tablesand Charts

• Tell the truth dont distort the data
• If the data is very simple, just use text
• Simplify
• If the story is simple, keep it simple.
• If the story is complex, make it look simpler
• Keep it Simple (for presentations)

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A complex graph is sometimes the best way to tell
a story
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The Cognitive Style of PowerPoint (Edward Tufte)

• How Not to Use PowerPoint
• Bullet Points are bad
• Style no substitute for content
• 40 words 8 seconds of silent reading very
  little actual content

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Analytics According to Captain Kirk

• PowerPoint does not provide enough detail for
  analysis
• One needs to look at all of the data to do a
  proper analysis

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Clarification Simple