Data Presentation

Adapted by Joanna Wolfe from Marianne W. Zawitz, Bureau of Justice Statistics, October 11, 2000

Presenting effective Tables and Figures

This presentation covers the principles of creating good technical graphs and tables.

1. Provide descriptive captions.

2. Consider your “story” and audience when presenting data.

3. Avoid non-data ink.

4. Be ethical: Persuade but do not deceive.

Always label tables and figures.

Figure 2: Recurrence of Gastric ulcers for the year after successful healing with ranitidine alone or triple therapy plus ranitidine. No maintenance was given.

Per

cent

wit

h U

lcer

Rec

urre

nce

Weeks

Graphs excel at emphasizing trends and relationships while tables display exact values in a small amount of space.

WeeksRanitidine

aloneTriple

therapy

4 8% 0%

8 20% 5%

16 42% 10%

24 60% 10%

Table 1: Recurrence of Gastric Ulcers by Therapy Type

Fig 2: Recurrence of Gastric Ulcers by Therapy Type

Line graphs are good for communicating change over time.

Bar graphs are good for communicating differences between values.

Pie charts are good for simple messages.

Bureau of Justice Statistics

Pie charts are bad for complex data or when precision matters.

Which slice is biggest?

Which is smallest?

By how much?

Bar charts allow readers to visualize differences between variables.

Which bar is biggest? Which is smallest?

By how much?

0 5 10 15 20 25

A

B

C

D

E

F

G

A 21B 19C 18D 14E 12F 9G 7

Tables allow readers to see EXACT differences between variables and exact values.

Which value is biggest? Which is smallest?

By how much?

The visualization expert Edward Tufte says "the only thing worse than a pie chart is two pie charts."

Which military branch grew the most between 1990 and 1998?

Bar charts simplify comparisons.

Which military branch grew the most between 1990 and 1998?

A 21B 19C 18D 14E 12F 9G 7

Which visualization is best for a technical audience?

0 5 10 15 20 25

A

B

C

D

E

F

G

Summary so far:

• Always supplement tables and figures with text: label axes and provide an informative caption.

• Use bar charts or tables to compare values.• Use line graphs to show trends.• Use tables when exact values are important.• Only use pie charts for simple data and non-

technical audiences.

Strive for simple designs that show the data.

Avoid non-data ink.

Avoid 3D.

1986 1987 1988 1989 19900

20

40

60

80

100

120

140

160

Administrative forfeituresMillions

3D charts add non-data ink and are more difficult to read than 2D charts.

Is 1987 above or below 60 million? What about 1988? 1990?

1986 1987 1988 1989 19900

20

40

60

80

100

120

140

160

Administrative forfeitures

Millions

Hidden data is a common problem with 3D presentations of 2D data

Bureau of Justice Statistics

A simple line chart in 2 dimensions avoids hiding data

West

South

NortheastMidwest

Bureau of Justice Statistics

The purpose of a chart is to convey data so avoid non-data ink.

Grids Ticks Frames Anything that does not convey data

1989 1990 1991 1992 1993 1994 1995 19960

10

20

30

40

50

60

70

Bureau of Justice Statistics

1989 1990 1991 1992 1993 1994 1995 19960

10

20

30

40

50

60

70

13-14

15

16

17

18 years old

Age of offender

Bureau of Justice Statistics

Excess tick marks can make charts hard to read.

13-14

15

16

17

18 years old

Age of offender

Bureau of Justice Statistics

Removing tick marks make trends easier to see.

ImplementationBefore implementation

After implementation

Average vehicle speed 45.5 mph 45.7 mphStandard deviations in vehicle speed

9.4 mph 7.2 mph

Implementation Before AfterAverage vehicle speed 45.5 mph 45.7 mphStandard deviations in vehicle speed 9.4 mph 7.2 mph

Tables also benefit from minimizing non-data ink.

Compressor Efficiency score

LZOP 1

PAR 1

PKZIP 1

JAR .99

WINACE .98

WINZIP .97

STUFFIT .90

DEEPFREEZE .91

HUFFMANCE .91

OPAQUE .71

BLINK .58

Tables also benefit from minimizing non-data ink.

Compressor Efficiency score

LZOP 1

PAR 1

PKZIP 1

JAR .99

WINACE .98

WINZIP .97

STUFFIT .90

DEEPFREEZE .91

HUFFMANCE .91

OPAQUE .71

BLINK .58

Criminal history of detained vs. released felony defendants, 1990

Series1

0 10 20 30 40 50 60 70 80 90

Detained

Released

Percent of felony defendants

Prior criminal history

Arrest

Any conviction

Felony conviction

Violent felony conviction

Avoid hatched fill patterns, which are hard to look at.

Se-ries1

0 10 20 30 40 50 60 70 80 90

Percent of felony defendants

Weapons arrest rate by age of offender

0

250

500

750

1000

1250

1500

1750

2000

2250

1965 1970 1975 1980 1985 1990

17-1815-1613-14

Stacked bars are also confusing.

Bureau of Justice Statistics

"Simplicity of design and complexity of data"

Edward R. Tufte