In this visualization we show how competition between test centers over students can lead to unused capacity. This unused capacity can lead to increases in testing costs (per student) for ACT because of the additional overhead of testing at large institutions. We illustrate this local competition with a network visualization small multiples grid of several cities over time. Each city’s grid is arranged to show the testing year as rows and the testing month as columns. This allows us to see, in general, patterns that occur sequentially, or cyclically (such as only occurring in September).
Within each grid cell is a network visualization that shows each testing center’s competition, which we derived from the geospatial coordinates of the testing center. Specifically, we calculated a Delaunay triangulation of these coordinates, filtered out edges with long distances, but ensured the network’s minimum spanning tree remained. This gives us a reasonable network model of what testing centers would be in competition with each other over students. We found the layout of this network using GraphViz’s neato algorithm.
We overlay two variables on top of this network visualization, ASSIGNED and CAPACITY, to show how students attend different test centers over time. These variables are encoded as the area of the circle. Test centers with large amounts of unused capacity will appear as white circles, whereas centers with near optimal capacity will appear nearly solid. Our visualization technique allows the reader to easily spot anomalies and hypothesize about where and why local competition for students may be occurring at test centers. For example, using our visualization and layout, we were able to quickly determine that test center 2270447 in McAllen Texas has a cyclic pattern of unused capacity. It’s also easy to see that North Metro in Georgia had an issue with unused capacity up until June of 2013, but hasn’t had an issue since then.
Dustin Arendt, firstname.lastname@example.org Meg Pirrung, email@example.com Pacific Northwest National Laboratory 902 Battelle Blvd. Richland, WA 99354