How (not) to lie with visualization

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How (not) to lie with visualization cs5764: Information Visualization Chris North

description

How (not) to lie with visualization. cs5764: Information Visualization Chris North. How (not) to lie with visualization. Show and tell “USA Today” graphs…. Stock Market Crash?!. Market. $9000 8875 8750 8625 8500. 199519961997199819992000. Showing entire scale. Market. - PowerPoint PPT Presentation

Transcript of How (not) to lie with visualization

Page 1: How (not) to lie with  visualization

How (not) to lie with visualization

cs5764: Information Visualization

Chris North

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How (not) to lie with visualization

• Show and tell

• “USA Today” graphs…

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Stock Market Crash?!

1995 1996 1997 1998 1999 2000

$9000

8875

8750

8625

8500

Market

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Showing entire scale

$10,000

7500

5000

2500

0

Market

1995 1996 1997 1998 1999 2000

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Shown in context

1950 1960 1970 1980 1990 2000

$10,000

7500

5000

2500

0

Market

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Another example

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Percentages: 0% – 100%Employment rate = 100 – unemployment rate

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Tufte’s Rule

• Visual attribute value should be directly proportional to data attribute value

• Lie factor = (visual effect) / (data effect)

• truth = 1.0

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Company financial status

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The hidden 0-points

• Lie factor = ?

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Changing Scale

13

0.5?

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ChangingScale

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…with linear time scale

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Down = Bad ?

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Make it explicit

B

ette

r

Other examples: user performance, questionnaire results

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Logarithmic data log scale

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Size Encoding

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Size Encoding: height or area?

= ?

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Size Encoding

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Height or Area

• Height = valueWidth = valueArea = value2

or

• Area = valueheight*width = valueheight = width = value 0.5

Problem:Using 2 dimensions to represent 1 dimension.

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Volume encoding?

Height?Diameter? Surface area?Volume?

73 – 79 data difference = 5.5x73 – 79 volume difference = 270x

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Problem with size encoding

1 2 3 4 5 6 7

Height

Area

Volume

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Height & width encoding1 2 3 4 5 6 7

Height

Height & Width

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Solution: just use height

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Size Encoding

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A Propaganda Classic

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Hmmm…

• Low rank = good!

• Different time scales

• Not really tuition

• Artistic mood

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How not to lie

• Show entire scale

• Show data in context

• Consistent, linear scale• Log scale for log data

• Up vs. down: indicate direction of improvement

• Avoid size encoding• Use height OR width

• Don’t use both for same data attribute

• Avoid area, volume encoding

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Visualization = Communication

• Communication is person dependent

• People have a lot of “baggage”

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Expectations

Parisin the

the spring

Lifeis a

a highway

Nowis the

the time

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Re-training

• Red spades, black hearts

• Poor user performance even after being told

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Orientation

• Who are they?

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Orientation

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Verbal-visual conflict

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Fun with illusions

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Is the grid OK?

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 Can you see gray squares?

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A man playing saxophone or a woman’s head?

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A head or a boy?

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2, or 1 face?

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Duck facing left or hare to the right?

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Horrible!!! A woman before the mirror??

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Young or old lady?

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It is said there are nine faces in this picture

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Will you go through it from left to right or from right to left?

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One vase or two faces?

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Can you build this?

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Where is the high land?