The alert that proves less than it seems
A sensitive signal can generate many false alarms when its target is rare.
What we know
- Fictional model: 1% of archive objects carry a special mark. A scanner flags 99% of marked objects and also 5% of unmarked objects. A flag is not confirmation.
- Use expected frequencies among 10,000 objects. For the third decision, assume two scanners with the same rates and errors independent conditional on whether an object is marked. That independence is an exercise assumption.
How to answer
Choose the conclusion best supported by the facts and press Check. You can revise an incorrect answer and use help whenever you wish.
Preparing the case…