Type of activity: In-class, small-group

Statistical topics: diagnostic testing, conditional probabilities

Time needed: 10 minutes

Materials needed:

• An activity form (HTML Version)
• A home pregnancy kit (not necessary, but helpful in introducing the activity)

1. Introduce the activity by reading the reported accuracy of the home pregnancy test.
2. Ask students to work with at least one other student.
3. Give one activity form to each student.
4. Ask students to study the two-way table and analyze the data.
5. Ask the students to answer the questions on the activity form to determine the accuracy of a pregnancy test.

After the students have completed the activity, the class should come back together as a group to discuss the purpose of the activity. The instructor can initiate the discussion by asking the students what they learned in doing this activity.  Points to include:

• the accuracy of a diagnostic test during development is not necessarily the accuracy of a diagnostic test in use
• P(A|B) does not necessarily equal P(B|A)
• low prevalence of disease contributes to high false positive rates.
• screening tests generally have high negative predictive values but low positive predictive values.

Comments from others who have tried activity:  None.

Supplementary materials:  Activity Form: HTML Version