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Visual Display of Data. Brad McMillen Evaluation and Research Department. 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?. Example.

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visual display of data

Visual Display of Data

Brad McMillen

Evaluation and Research Department

things to consider
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?

example
Example

Taken from http://www.cdc.gov/nccdphp/dnpa/obesity/trend/maps/index.htm

slide4
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%.

table
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
bar column chart
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
line chart
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
pie chart
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
scatterplot
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
histogram
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
principles of good graphics
Principles of Good Graphics
  • Clearly labeled
  • Not too “busy”
  • Readable font
  • Quickly draws attention to the desired point
  • Reasonable choice of metric and precision
example26
Example

Taken from http://www.cdc.gov/nccdphp/dnpa/obesity/trend/maps/index.htm

sources of deception in graphics
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
slide30

Taken from Tufte, E. (1983). The Visual Display of Quantitative Information. Cheshire, CT: Graphics Press.

slide36
Brad McMillen

Evaluation and Research Department

Wake County Public Schools

bmcmillen@wcpss.net

(919) 850-1903