McKinley: A double-blind study, in which neither the patient nor the primary researcher knows whether the patient is being given the drug being tested or a placebo, is the most effective procedure for testing the efficacy of a drug  But we will not be able to perform such a study on this new drug, since the drug will have various effects on the patients' bodies, which will make us aware of whether the patients are getting the drug or a placebo
Engle: You cannot draw that conclusion at this point, for you are assuming you know what the outcome of the study will be
referring to the drug's therapeutic effects rather than to any known side effects