### Home > CCA2 > Chapter 11 > Lesson 11.3.1 > Problem 11-88

Any system that is responsible for detecting relatively rare events is going to have problems with false positives. You saw this in problem 11-86 regarding testing for HIV. Consider other cases such as burglar alarms, smoke detectors, red light cameras and drug testing for athletes. All of these systems have proven accuracy and all have a persistent problem of false positives (false alarms).

Consider a hypothetical situation. Suppose that rare event A occurs with a frequency of

Make a model for this situation.

Make a two-way table or tree diagram.

Your model should have labels:

Event A: yes or no

Alarm sounds: yes or noIf the alarm has been activated, what is the probability that it is false?

Are the test results mathematically independent of whether event A occurs or not? How could you check this? Explain.

Does the accuracy of the alarm sounding depend on Event A occurring?