In a double-blind experiment designed to test the effectiveness of a new medication as a treatment for lower back pain, 1643 patients were randomly assigned to one of three groups: (1) the 547 subjects in the placebo group were given pills containing no medication; (2) 550 subjects were in a group given pills with the new medication taken at regular intervals; (3) 546 subjects were in a group given pills with the new medication to be taken when needed for pain relief.

What does it mean to say that the experiment was "double-blind"?

Choose the correct answer below.

A.

Both the subjects in the study and those who administered the pills knew whether they were taking a placebo or the new medication.

B.

The subjects in the study did not know whether they were taking a placebo or the new medication, and those who administered the pills also did not know.

C.

The subjects in the study were given the choice of taking the placebo or the new medication, but those who administered the pills did not know which group the subjects were in.

D.

The subjects in the study did not know whether they were taking a placebo or the new medication, but those who administered the pills did know.