PSY 1950Graph Design

December 8, 2008

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Why graph?• Exploratory data analysis

– Usually raw data– Tukey: a good graph “forces us to notice

what we never expected to see”– e.g., scatter plot, funnel plot– Design less important

• Communication– Usually summary statistics– “a picture is worth a thousand words”– e.g., line graphs, bar graphs– Design extremely important

Bar Graphs vs. Line Graphs• Bar graphs

– Convey position (i.e., bar height)• Effective in conveying relative point values• Ineffective for conveying interaction effects

– X axis has nominal or ordinal scale

• Line graphs– Convey change in position (i.e., line

slope)• Ineffective in conveying relative point values• Effective for conveying interaction effects

– X axis has interval or ratio scale• Okay for 2-level nominal scale

Values vs. Trends

Relevance• Communication is most effective

when neither to much nor too little information is presented

• Tufte (1983): “Maximize the data-ink ratio, within reason”, where data-ink ratio is the “proportion of a graphics ink devoted to the non-redundant display of data.”

Distracting Backgrounds

4

4.5

5

5.5

6

Control Experimental

Count

Men Women

4

4.5

5

5.5

6

Control Experimental

Count

Men Women

Appropriate Knowledge• Communication requires prior

knowledge of relevant concepts, jargon, and symbols

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4.5

5

5.5

6

Control Experimental

Score on Dependent Variable

Men Women

**

*

Jargon, Symbols

Concepts

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4.5

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5.5

6

Novel Suppress Concentrate

Stimulus Condition

Score on Dependent Variable

Meditators

Controls

-1

-0.5

0

0.5

1

Suppression Concentration

Priming Condition

Score on Dependent Variable

Meditators

Controls

Salience• Attention is drawn to large

perceptible differences

Discriminability• Two properties must differ by a large

enough proportion or they will not be distinguished

Size

0

1

2

3

A B

Group

Dependent Variable

0

1

2

3

A B

Group

Dependent Variable

Proportion

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2

3

A B

Group

Dependent Variable

0

1

2

A B

Group

Dependent Variable

Scale

Perceptual Organization• People automatically group elements

into units, with they then attend to and remember

Compatibility• A message is easiest to understand if

its form is compatible with its meaning

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4-5 Year Olds

7-8 Year Olds

9-10 Year Olds

Average Word Length

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4.5

5

5.5

6

4-5 Year Olds 7-8 Year Olds 9-10 Year Olds

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4.5

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5.5

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Control Experimental

Score on Dependent Variable

Women

Men

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4.5

5

5.5

6

Experimental Control

Score on Dependent Variable

Women

Men

Color, Category Placement

Between vs. Within Subjects

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4.5

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5.5

6

Control Experimental

Score on Dependent Variable

Men Women

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4.5

5

5.5

6

Control Experimental

Score on Dependent Variable

Informative Changes• People expect changes in properties

to carry information

3.5

4

4.5

5

5.5

6

6.5

Novel Suppress Concentrate

Stimulus Condition

Score on Dependent Variable3.5

4

4.5

5

5.5

6

6.5

Novel Suppress Concentrate

Stimulus Condition

Score on Dependent Variable

Capacity Limitations• People have a limited capacity to

retain and to process information and will not understand a message if too much information must be retained or processed

Placement is Key

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4.5

5

5.5

6

Novel Suppress Concentrate

Stimulus Condition

Score on Dependent Variable

Controls Meditators

4

4.5

5

5.5

6

Novel Suppress Concentrate

Stimulus Condition

Score on Dependent Variable

Meditators

Controls

Horizontal vs. Vertical Bars: Labels

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Amphetimines

Cocaine

Hashish or Marijuana

Heroin, opium, or morphine

LSD

Prescription drugs

Solvents

Percentage Use

0

5

10

15

20

25

30

35

Amphetimines

Cocaine

Hashish or Marijuana

Heroin, opium, or morphine

LSD

Prescription drugs

Solvents

Percentage Use

Font Typehttp://www.surl.org/usabilitynews/32/font.asp

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Font Typehttp://www.surl.org/usabilitynews/32/font.asp

QuickTime™ and a decompressor

are needed to see this picture.

Font Style• ALL UPPERCASE TEXT IS HARDER

TO READ than all lowercase text or Mixed Case Text

• Italicized text is harder to read than plain text

• Underlined text (e.g., pajamas) is harder to read than non-underlined text (e.g., pajamas)

Scatterplots

ExampleZachs, J., & Tversky, B. (1999). Bars and lines: A study of

graphic communication. Memory & Cognition, 27, 1073-1079.