W. H. R. Rivers is credited with creating the first double-blind experiment in 1907. Rivers was interested in finding out if caffeine has an effect on work output. He quickly discovered the psychological effect on subjects who knew they were receiving a treatment. This led him to create a - placebo for each experiment, which looked and tasted just like the caffeine treatment. Rivers would have a friend prepare the caffeine drinks and the placebo drinks and would then give the drinks to the subjects.

(a) Explain what it means for this experiment to be double-blind.

(b) Why was it important for this experiment to be double-blind?