We have a design for a new type of graphical display for the "goodness of fit" of IRT models to data, using "mosaic plots" which are two-dimensional displays of the correspondence between counted (frequency) data and models for such data. These graphics are sufficiently unconventional that they cannot be drawn by standard graphics "packages" that make such things as line plots and bar charts; one looks like this:

These mosaic plots must be computer graphics---they are too computationally intensive to be made by hand. These plots, if they could be made easily, would be very useful for folks doing large-scale educational test assembly---and that is a lot of folks who would use this (free) software if we make it (free).

Possible goal:

Design and build an application that reads "item parameter" files and test-data file files, and combines the two to create on-screen goodness of fit graphics. We have the specifications for the computations in prose equations, and examples of the graphics. Either Windows or the Mac OS would be a useful target; a design that looked forward to cross-platform future development would be most useful.

This project is not as well-defined as the Plotlog project. We have code-fragments---at one point, we had a limited version of the application running under the Mac OS, but that was about five versions of Metrowerks' compiler ago, and it likely won't compile any more. On the other hand, the project is more amenable to ground-up design.