# Bayes' Theorem

## Welcome to the class..

This GeoGebra worksheet can be used to explore the following problem, which is a classic application of Bayes' theorem: If a person tests positive for a disease, what is the probability that he or she is actually infected? The user can enter the following quantities by using the input boxes or the sliders: Incidence is the percentage of the general population that is infected. False positive rate is the probability that a person who is not infected will test positive for the disease. False negative rate is the probability that a person who is infected will test negative for the disease. The pie chart shows the conditional probability that a person is infected given that he or she tests positive for the disease.

## Welcome to the class..

This GeoGebra worksheet can be used to explore the following problem, which is a classic application of Bayes' theorem: If a person tests positive for a disease, what is the probability that he or she is actually infected? The user can enter the following quantities by using the input boxes or the sliders: Incidence is the percentage of the general population that is infected. False positive rate is the probability that a person who is not infected will test positive for the disease. False negative rate is the probability that a person who is infected will test negative for the disease. The pie chart shows the conditional probability that a person is infected given that he or she tests positive for the disease.

How do you calculate Bayes Theorem?

What must be the value of incidence of disease, false positive and false negative in order to have a probability of 50% that the person is infected?