McKinley explains that a double-blind study, one in which neither the patient nor the primary researcher knows whether the patient is being given the drug, is the most effective procedure for testing the efficacy of a drug.
However, the new drug will not be able to be tested in a double-blind study because "the drug will have various effects on the patients' bodies" that will make the researchers aware of whether the patients are getting the drug or a placebo.
Engle responds stating that McKinley cannot draw that conclusion (i.e. that the new drug cannot be tested with a double-blind study) because McKinley is assuming that he knows the outcome of the study.
However, that is not what McKinley is saying. McKinley says that they cannot use the double-blind because the drug will have various effects on the patients' bodies that will make the researchers aware of who is taking the drug. This is referring to side effects that the researchers know the drug will have, which will tip them off to who the drug-taking patients are. McKinley is not inferring that the researchers know the therapeutic effects, i.e. the end-result/conclusion of the drug's overall effects. Rather, he is merely explaining that due to their knowledge of various side effects that the drug has, the researchers will be made aware of who is taking the drug, which will not allow the drug to be tested under the conditions of a double-blind study.
Thus, answer choice (D) "referring to the drug's therapeutic effects rather than to any known side effects," is the correct answer.
Hope that helped! Please let us know if you have any other questions.
