### Start Here: Instructions for Herpes Test

There are several different viruses that can cause painful blisters,
including herpes and others. There are medicines that
are helpful against herpes. However, if the other virus
is mistakenly diagnosed, the medicine could cause complications,
so it is useful to test for herpes.
Suppose the older, less expensive test correctly gives
a “positive” test result in 70% of the cases of people with herpes and gives
a false “positive” result in 30% of the cases of people without herpes.
Suppose that there is a new expensive test for herpes simplex that
correctly gives a “positive” test result in 90% of the cases of people with herpes
and gives a false “positive” result in 10% of the cases of people without herpes.

Based on a patient's age and medical history the rate of
herpes varies. One group has a base rate of 20% and the other
has an 80% rate of having herpes without taking the test.

Scroll down and look at the trials below. Your task is to put the information together in each case to estimate the probability that the person actually has herpes, based on their medical history and up to two diagnostic tests, summarized at the left.

#### Warmup Trials Medical Decisions