Simulating the Classic Polya Urn Problem


This simple model simulates the classic Polya urn problem in which stones, either black or white, are randomly selected (with replacement) from a pot. The user begins with two stones, one of each color. Each time a stone of a given color is selected, the stone is replaced and another stone of the same color is added to the pot. Therefore, the odds of adding a stone of a given color is always equal to the proportion of that color currently in the pot. A Random Choice element, triggered on each timestep of the model, is used to model the random selection of a stone from a pot. A 'White' event from the Random Choice element triggers the addition of a white stone to the pot. A 'Black' event triggers the addition of a black stone.


Making Better Decisions In An Uncertain World