Answer: The double-blind procedure
Explanation:
Double blind procedure is one of the study in which the participants and also the experimenters are basically blind from the knowledge about some crucial topics and also from the study.
The double blind is basically refers to the procedure including the expectations and the hypotheses that plays an important role for preventing the useful study and also the demand charactertics.
According to the given question, the double blind procedure is one of the method that helps in prevent the expectations about the various types of brands effectiveness and also influencing from the experimental test.
Therefore, Double-blind procedure is the correct answer.