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.
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KUDOS me if you feel my contribution has helped you.

Straight B.

If the variation is due to regional difference, the notion that there is actual unnecessary prescription is weakened.

Cheers,
Der alte Fritz.
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+1 Kudos me - I'm half Irish, half Prussian.