What’s the Chance? Dependent and Independent Trials

Abstract

In many situations, people need the probability that a certain event will occur. For example, a public health inspector may need the probability that a well is polluted, a pollster may wish to find the probability that voters will favor limited terms for elected officials, or a quality-control manager may be interested in the probability that a product is defective in a continuous production process. As in most real-world situations, it is impossible to test all the wells, poll all the people, or check all the products. How can we estimate these probabilities, and how accurate can our estimates be? We will use a thumb tack as our prototype and see how we can estimate the probability that a tack lands point down.