Answer:
The placebo effect
Explanation:
The placebo effects is an improvement in the area of health and behavior that is measurable and cannot be attributed to a treatment or medication. From the example in the question, coffee drinking may cause participants to become anxious, just because they are of the belief that coffee would make them anxious. Hence the decaffeinated coffee would not allow the subjects know the type of Coffee they are taking, this can help Dr. Wilkins to control this effect.
