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.

The user can enter the following quantities by using the input boxes or the sliders:

Incidenceis the percentage of the general population that is infected.False positive rateis the probability that a person who is not infected will test positive for the disease.False negative rateis 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.

Comments or suggestions are welcome. Enjoy!

Addendum:Dave Richeson had a similar idea.Download: