It is illegal to advertise prescription medications in Hedland except directly to physicians, either by mail or in medical journals. A proposed law would allow general advertising of prescription medications. Opponents object that the general population lacks the specialized knowledge to evaluate such advertisements and might ask their physicians for inappropriate medications. But since physicians have the final say as to whether to prescribe a medication for a patient, inappropriate prescriptions would not become more common.
Which of the following would it be most useful to establish in order to evaluate the argument?