Displaying and

1

• Displaying and
• Communicating Data

Connie Satzler
2
Objectives

• Identify types of data displays and their most
  appropriate uses
• Recognize inappropriate and misleading uses of
  data displays
• Evaluate and plan your own effective use of data
  displays

3
This presentation

• Includes intuitive deceptively simple
  conceptsnot always practiced in professional
  publications
• Based on research in the disciplines of..
• Human factors/ergonomics
• Statistics
• Geography, particularly cartography
• Also draws from our own personal experiences and
  biases

4
The Purpose of Data Displays

• To communicate information
• A tool to aid in the analysis of data

5
Graphics reveal data.
6
Goal of Data Displays

• To make patterns, relationships, disparities, and
  exceptions obvious at a glance.

7
Example John SnowMap of cholera outbreak
8
The Geographical Journal
9
Types of Data Displays

• Table
• Organized presentation of numbers and/or text,
  generally in rows and columns
• Graph
• Pictorial representation of quantitative
  information
• Map
• Spatial or geographic representation of
  quantitative or qualitative information

10
Graph or Table?

• Graphs have the edge when
• The displayed data have an inherent structure and
  the structure is relevant
• The user is interested in general comparisons and
  relationships
• The user is interested in comprehending a large
  set of numbers (gt 20) at-a-glance

• Tables have the edge when
• Exact numbers are needed
• The user is analyzing or comparing a small set of
  numbers (lt 20)

11

• Graph or Table?

12
1996 Kansas Traffic Accident Facts
13
1996 Kansas Traffic Accident Facts
14
Kansas Annual Summary of Vital Statistics 2000
15
Guidelines for PresentingData in Tables
16
Avoid using more significant digits than
necessary.
Kansas Hospital Association 2002 STAT Book
17
Use explicit rather than implicit tables (i.e.,
give the user the numbers they need).
Kansas Annual Summary of Vital Statistics 2000
18
Guidelines for PresentingData in Tables

• Avoid using more significant digits than
  necessary.
• Use explicit rather than implicit tables (i.e.,
  give the user the numbers they need).
• Facilitate comparisons
• Make primary comparisons down columns (rather
  than across rows).
• Logical grouping is generally better than
  alphabetical.
• The lower the usage of a column, the farther to
  the right it should be.

19
Guidelines for PresentingData in Tables

• Within a column...
• If all else is equal, place larger and/or high
  usage data on top.
• Use decimal-point alignment.
• Reduce row alignment errors.
• Group rows with spaces, lines, or shading.
  (Avoid heavy grids.)
• Reduce horizontal distance between columns.
• Use dotted leader lines.
• Include averages and/or totals for rows and
  columns.

20
Facilitating comparisons. Row and column
guidelines.
Kansas Annual Summary of Vital Statistics 2000
21
Which table is better and why?
22
Principles of Graphical Integrity

• Above all else show the data.

Edward Tufte, 1983
23
Principles of Graphical Integrity

• Clear, detailed, and thorough labeling should be
  used to defeat graphical distortion and
  ambiguity.
• A graphic does not distort if the visual
  representation of the data is consistent with the
  numerical representation.
• Show data variation, not design variation.
• Graphics must not quote data out of context.

24

• All pictures tell a story,
• but not all stories are true.

25
Clear, detailed, and thorough labelingshould be
used to defeatgraphical distortion and
ambiguity.
Profile of Health Disparities Among Communities
of Color, Colorado 2001
26
A graphic does not distort if the visual
representation of the data is consistent with the
numerical representation.
Los Angeles Times, August 5, 1979, as reprinted
in The Visual Display of Quantitative
Information, 1983