One hundred volunteers who suffer from severe depression are available for a study. Fifty are selected at random and are given a new drug that is thought to be particularly effective in treating severe depression. The other fifty are given an existing drug for treating severe depression. A psychiatrist evaluates the symptoms of all volunteers after four weeks in order to determine if there has been substantial improvement in the severity of the depression.

(a) The factor in this study is

A. the use of randomization and the fact that this was a comparative study.
B. which treatment the volunteers receive.
C. the use of a psychiatrist to evaluate the severity of depression.
D. the extent to which the depression was reduced.

(b) Suppose the volunteers were first divided into men and women, and then half of the men were randomly assigned to the new drug and half of the women were assigned to the new drug. The remaining volunteers received the other drug. This would be an example of

A. replication.
B. a matched pairs design.
C. confounding. The effects of gender will be mixed up with the effects of the drugs.
D. a block design.

(c) The study would be double blind if

A. neither drug had any identifying marks on it.
B. all volunteers were not allowed to see the psychiatrist nor the psychiatrist allowed to see the volunteers during the session in which the psychiatrist evaluated the severity of the depression.
C. neither the volunteers nor the psychiatrist knew which treatment any person had received.
D. All of the above.