A surgeon developed a new procedure for knee replacement surgery. In order to determine the effectiveness of the surgery, s/he recruits fifty pateints for a double-blind study. The surgeon randomly assigns each volunteer to receive either the new procedure or the standard procedure. S/he monitors each patient after the procedure is completed to determine if one group has better outcomes than the other.

What does it mean for this experiment to be double-blind?

a. Both the volunteers and the surgeon are unaware of who is receiving the new procedure and who is receiving the standard procedure.

b. The surgeon is unaware of which surgery each volunteer receives.

c. The volunteers are unaware of which surgery they receive.

d. The volunteers are unaware of what is being measured in the experiment.

e. The surgeon is unaware of what is being measured in the experiment.