A researcher has a sample of 30 rats that are all cloned from the same source. The 30 rats are genetically identical and have been raised in exactly the same environment since birth. The researcher conducts an experiment, randomly assigning 10 of the clones to treatment A, 10 to treatment B, and the other 10 to treatment C.
Explain why the clone experiment is better than a within-subjects study using 10 regular rats that are tested in each of the three treatments.
In other words, explain how the clone experiment eliminates the basic problems with a within-subjects study.