What does 'double-blind' mean here?
A pharmaceutical company has begun a large trial of a new vaccine. Ten thousand volunteers are taking part. Half receive the vaccine, and half receive a harmless placebo, but neither the volunteers nor the staff who give the injections know who has received which. This method is called a double-blind trial. After six months, the company will compare how many people in each group became ill. Independent experts will check the results before the vaccine can be approved.
Answer and explanation
Correct answer: D. Nobody involved knows who got the vaccine
- Step 1: Both volunteers and staff giving injections are unaware. Answer: Nobody involved knows who got the vaccine. Why not the others: The other options do not describe the method.
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