Optimizing the Visual Presentation of Your Data

Optimizing the Visual Presentation of Your Data

Mary Beth Hasselquist, MD

#stc15

Graphs constructed using principles derived from knowledge of visual science present •  the user with easy-to-perform visual

tasks and •  a visual message that’s congruent with

the intended message.

© 2015 Aktiva Design, Mary Beth Hasselquist

Designers encode data. Users visually decode the data. A graph is successful only if the decoding process is effective. Different types of graphs require different tasks to decode the data.


Position along a common scale Position along identical, nonaligned scales Length

Angle Slope

Area (and volume)

Color value


Decoding tasks from most accurate to least accurate

605040302010

54.1

12.6

8.6

7.9

7.5

5.3

3.2

0.8

100%

Percent

A user is able to more accurately decode data from a bar (or column) graph than from a pie chart.


Column and bar graphs encode data in two ways: •  Length •  Position along a common scale

In order to encode the data accurately, column and bar charts must start at zero.


Incorrect construction!


This column is 40% as long as this column.

This column is 85% as long as this column.

60

50

40

30

20

10

010 20 30 40

Predicted probability of adherence (%)

Copayment for 30-day supply of statin (USD)

Adherence to Statin Medication by Copayment


60

50

40

30

20

10

010 20 30 40


Copayment for 30-day supply of statin (USD)


44

46

48

50

52

54

56

58

60

10 20 30 40Copayment for 30-day supply of statin (USD)



If the intended purpose of a graph is to highlight the differences between the variables and a column (or bar) graph doesn’t meet this intended purpose, a point (dot) graph can be used. Point graphs encode data using position along a common scale.


5.1%16.0%

The addition of numerals at the top of columns (or the ends of bars) adversely effects decoding of the data.

Visually, the addition of numerals lengthens the columns.

The left column is about two thirds as tall as the right.

The left column is about one third as tall as the right.

Visually, these two columns look more like this than this.


Gestalt principle of Proximity Items that are closer together will appear to belong together as compared to items that are further away.

Comp EPO HMOPOS PPO POS w/caCDHP HDHP Unknown

item 1item 2item 3

item 4item 5item 6

item 7item 8item 9

not Comp EPO HMOPOS PPO POS w/caCDHP HDHP Unknow

item 1item 4item 7

item 2item 5item 8

item 3item 6item 9


Construct graphs so that the visual message is congruent with the intended message.

A

10

0

5

15

Study population (%)TreatmentNo treatment

DCBA

10

0

5

15

Study population (%)No treatmentTreatment

DCB

Intended message: Treatment reduces risk compared to no treatment.

visually incongruent with intended message

visually congruent with intended message


Whenever possible, construct graphs so that the math is done for the viewer.

A

10

0

5

15

Study population (%)No treatmentTreatment

DCB

3.02.52.01.51.00.50

Absolute Risk Reduction of Treatment

B

A

C

D

Absolute risk reduction (%)

In this graph, users must visually do the math to determine the difference between no treatment and treatment for each category.

In this graph, the math has been done for users. © 2015 Aktiva Design, Mary Beth Hasselquist

Employing 3D effects, gradients and shadows is almost always a poor design choice when constructing graphs.


Design principles •  Use horizontal text within graphs

whenever possible for easier reading •  Order categorical data in a way that is

instructive, not arbitrary •  Use an appropriate scale


Hue

Saturation

Value

Color has three dimensions


Hue has no semantic meaning. Any meaning associated with a given hue is culturally determined.


Values have semantic meaning. These meanings are universal.

Least

Most


Adobe Illustrator default Better


3.02.52.01.51.00.50

Absolute Risk Reduction of Influenza-Related Complications 30-Days after Influenza Diagnosis in Children with Chronic Medical Conditions Provided by Antiviral Treatment with Oseltamivir

Influenza-related complication

Respiratory illness other than pneumonia

Otitis media and related complications

Pneumonia

Hospitalizations—all-cause

Hospitalizations—pneumonia-related

Hospitalizations—non-pneumonia respiratory illness

Absolute risk reduction (%)3.02.52.01.51.00.50

Absolute Risk Reduction of Influenza-Related Complications 30-Days after Influenza Diagnosis in Children with Chronic Medical Conditions Provided by Antiviral Treatment with Oseltamivir

Influenza-related complication

Respiratory illness other than pneumonia

Otitis media and related complications

Pneumonia

Hospitalizations—all-cause

Hospitalizations—pneumonia-related

Hospitalizations—non-pneumonia respiratory illness

Absolute risk reduction (%)

Use color purposefully and only when it contributes to the effectiveness of the graph.

A A

C

B

E

D

F F

E

D

C

B

In this graph, color has no intended purpose other than to make the graph “colorful.” The use of mul:ple colors degrades the pa;ern.


Any image created in color must work in grayscale. •  Color documents are often reproduced

in grayscale. •  Certain visual information, such as information

about figure and ground, is carried to the brain only in grayscale.


Because the values of some colors are similar, when the chart is reproduced in grayscale, it is difficult to distinguish the different wedges.


In order for us to easily read, there must be sufficient contrast between figure (text) and ground (background).




Mary Beth Hasselquist, MD [email protected] 206-660-9474


Data & Analytics

Optimizing the Visual Presentation of Your Data