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

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

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

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

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

16. Percent of Students Proficient Geometry 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

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

24. # Students by Ethnicity

25. Report Cards

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

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

29. Taken from http://mediamatters.org/items/200503220005

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

36. Brad McMillen Evaluation and Research Department Wake County Public Schools bmcmillen@wcpss.net (919) 850-1903