Vaccinated in Hospital

Counts versus rates

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• When coverage is high, many cases can be vaccinated even with a good vaccine.
• Compare rates within groups, not raw counts: the base-rate fallacy.
• With 90% efficacy, half of patients are vaccinated at about 91% coverage.

Steps

1. A puzzling headline
2. A town of 1,000
3. Rising coverage
4. The right comparison
5. Read the rates
6. Work out the efficacy