Select the best answer. Two essential features of all statistically designed experiments are

(a) compare several treatments; use the double-blind method.

(b) compare several treatments; use chance to assign subjects to treatments.

(c) always have a placebo group; use the double-blind method.

(d) use a block design; use chance to assign subjects to treatments.

(e) use enough subjects; always have a control group.

Answer: (e) use enough subjects; always have a control group. Two essential features of all statistically designed experiments are enough subjects and a control group.

Explanation

Statistically designed experiments have three essential features: Replication, randomization, and control.

Replication means that we need to replicate the experiment with multiple subjects and thus we need to use enough subjects.

Randomization means that we obtain randomization by randomly selecting our subjects or randomly assigning the subjects to treatment groups.

Control means that we require a control group (which could be a placebo group, but a placebo group is not always required such as when dealing with plants/animals).

We then note that answer option (e) best fits the essential features, as it refers to replication and control.