Question

A double-blind study of a vaccine is one in which :The study group receives the vaccine and the control group receives a placebo.Neither observer nor subjects know the nature of the placebo.Neither observer nor subjects know which subject receives the vaccine and which receives a placebo.Neither the study group nor the control group knows the identity of the observers.The control group does not know the identity of the study group.

Answer 1

Neither observer nor subjects know which subject receives the vaccine and which receives a placebo

Step-by-step explanation:

In a double-blind study neither the participants nor the experimenters is aware of who is receiving a particular treatment.

Its used to prevent bias in research results from demand characteristics or the placebo effect