Use of external visual representations in probability problem solving

We investigate the use of external visual representations in probability problem solving. Twenty-six students enrolled in an introductory statistics course for social sciences graduate students (post-baccalaureate) solved eight probability problems in a structured interview format. Results show that students spontaneously use self-generated external visual representations while solving probability problems. The types of visual representations used include: reorganization of the given information, pictures, novel schematic representations, trees, outcome listings, contingency tables, and Venn diagrams. The frequency of use of each of these different external visual representations depended on the type of probability problem being solved. We interpret these findings as showing that problem solvers attempt to select representations appropriate to the problem structure, and that the appropriateness of the representation is determined by the problem's underlying schema.