Visual Display of Data

1
Visual Display of Data

• Brad McMillen
• Evaluation and Research Department

2
Things to Consider

• Choices
• Text
• Tables
• Charts/Graphs
• What do you want to say?
• Who are you saying it to?
• What is the most concise way to say it?

3
Example
Taken from http//www.cdc.gov/nccdphp/dnpa/obesity
/trend/maps/index.htm
4
Text

• Between 1996-97 and 2006-07, the number of
  students enrolled in WCPSS grew by 50. During
• that same time, however, the number taking AP
  exams increased by 175 and the number of exams
  taken increased 195.

5
Table

• Simple, but effective
• Can be one or two-dimensional (rows and/or
  columns)
• Good for displaying smaller (or larger!) amounts
  of data
• Layout of table can determine how the audience
  consumes the data

6
(No Transcript)
7
(No Transcript)
8
Bar/Column Chart

• Usually used to show changes over time or
  comparisons among groups/categories
• Clustered Column - compares values across
  categories
• Stacked Column - shows the relationship of
  individual items to the whole
• 100 Stacked Column - compares the percentage
  each value contributes to a total across
  categories

9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
Line Chart

• Shows changes or trends over time
• Either for a single category or multiple
• Horizontal axis usually is a time measurement
• Usually with equal intervals of time

13
(No Transcript)
14
Pie Chart

• Shows the proportionality across categories as
  they relate to a whole
• Pie - displays the contribution of each value to
  a total
• Exploded Pie - displays the contribution of each
  value to a total while emphasizing individual
  values

15
(No Transcript)
16
Percent of Students ProficientGeometry EOC Test,
2006-07
17
Scatterplot

• Shows pairs of values plotted according to
• X-Y coordinates
• Good for illustrating the relationship between
  two variables
• Good for displaying the amount of spread in the
  data

18
(No Transcript)
19
(No Transcript)
20
Histogram

• A chart (usually a simple column chart) that
  takes a collection of measurements and plots the
  number of measurements (called the frequency)
  that fall within each of several intervals

21
Distribution of EOG Scale Scores
22
Principles of Good Graphics

• Clearly labeled
• Not too busy
• Readable font
• Quickly draws attention to the desired point
• Reasonable choice of metric and precision

23
(No Transcript)
24
Students by Ethnicity
25
Report Cards
26
Example
Taken from http//www.cdc.gov/nccdphp/dnpa/obesity
/trend/maps/index.htm
27
Sources of Deception in Graphics

• Labels not specific
• Scaling of axes is inappropriate
• Choice of chart type leads reader to the wrong
  conclusions
• Ignores important contextual factors
• Too much stuff obscures the point

28
(No Transcript)
29
Taken from http//mediamatters.org/items/200503220
005
30
Taken from Tufte, E. (1983). The Visual Display
of Quantitative Information. Cheshire, CT
Graphics Press.
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36

• Brad McMillen
• Evaluation and Research Department
• Wake County Public Schools
• bmcmillen_at_wcpss.net
• [phone]