Dice Stalagmite is an interactive computer-based model. The model is part of the ProbLab curriculum designed by Dor Abrahamson initially at Uri Wilensky's Center for Connected Learning and Computer-Based Modeling (CCL) at Northwestern University and later at UC Berkeley. The EDRL website features some of these latter models as relevant to our publications. We are grateful to the CCL for continued technological support and version updates.
Dice Stalagmite is a model for thinking about the relations between independent and dependent random events. Pairs of dice are rolled, then the dice fall into columns in two bar charts. One of these charts records the dice as two independent outcomes, and the other, as a single compound event (sum) of these two outcomes. Because the columns grow from the bottom up, we call this a "stalagmite."
Different distributions emerge: the independent-event bar chart is flat (equally distributed) whereas the dependent-event bar chart is peaked. (It does not quite approach a normal distribution, because there are only two compound outcomes.)