An investigator evaluated the effectiveness of a therapy on three types of patients. She collected the following improvement ratings, but these data form skewed distributions.

(a) Which procedure should be used? Why?
(b) What should the investigator do to the data first?
(c) If the results are significant, what should she do next?
(d) Ultimately, what will we learn from this study?

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Manic Schizophrenic 16 13 12 20 21 10 15