The rate at which psychiatrists in different regions

The rate at which psychiatrists in different regions administer many prescription drugs shows massive variation — up to a fifty-fold dissimilarity per million patients in the numbers of antidepressant, anti-bipolar, and anti-psychotic medications prescribed.

To support a conclusion that much of the variation is due to unnecessary prescription of drugs, it would be necessary to establish which of the following?

A: Every psychiatrist is supervised by a regional review board, which checks the record of every patient to confirm that the prescription drug was necessary.

B: The dissimilarity is unrelated to regional factors (other than the prescription drugs themselves) that influence the incidence of diseases for which prescription drugs might be considered.

C: There are several classes of prescription drugs (other than antidepressant, anti-bipolar, and anti-psychotic ones) that are often administered unnecessarily.

D: For certain prescription drugs, it is difficult to determine after the treatment whether the drug was necessary or whether an alternative treatment would have been effective.

E: The prescribing of antidepressant, anti-bipolar, and anti-psychotic drugs is representative of prescription drugs generally with respect to how often they are prescribed unnecessarily.