Monday, January 08, 2007

Graphics that Work for Data Analysis

Edward Tufte's fourth grand principle regarding effective visual display of quantitative information is to "completely integrate words, numbers, and images". Tufte is imploring report writers to ensure that the text that explains a graphic is on the same page as the graphic. Tufte is also arguing that the person observing the graphic should not be required to learn a system to understand the meaning. In some cases there is background knowledge required to make sense of the information being displayed, the amount of background required should be the bare minimum of the likely readers. In creating effective graphics for use by teachers and administrators I can assume a minimal understanding required to perform those jobs. Teachers will know what a "scale score" and "proficiency level" while the average member of the public may not.

Here is a sample of simple excel graph that takes into account the fourth grand principle. It displays the scores in a simple way with the data table below. It completely integrates the visual and the data. The visual leaves something to be desired, so I have two more graphics to discuss.

The next two graphics are include a good example of the fourth principle and a poor example of the fourth principle. Both examples were the result of projects where I designed the visuals. The first example comes from a custom data analysis portal designed by Adams County School District 14 staff to analyze NWEA MAP data and the results of the Colorado Student Assessment Program (CSAP). The portal has been a smashing success with our targeted end users (teachers). We hear frequently how access to data in a convenient and user-friendly format has enabled teachers make decisions informed by student data. However, one complaint we have received is that where teachers can drill down to look at sub-scores for a test period the goal areas are not defined (see graphic below). It simply says, "goal 1". Users have to open a PDF document that translates the goal to language such as "number sense". Tufte artriculates that these words should be completely integrated and teachers should not be forced to open a new document and toggle between the two.

The graphic below displays the results for an individual student on the Colorado English Language Acquisition assessment (CELA). The test returns seven total scores and many sub-scores. A reader of this report knows instantly how a student performed overall and in each of the sub-areas. There is little question and absolutely no necessity to toggle to a key. The words, colors, and symbols clearly direct the reader to a usable description of student performance. See more examples of CELA reports here.

The CELA graphic more clearly allows the user to kick butt at what they do best, teaching. The portal display example encourages users to kick butt at toggling between documents or memorizing the goal area descriptions. Which would you rather have happen in your schools?

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