Dr. Wilkins randomly assigns subjects to one of two groups. He is interested in the effects of caffeine on anxiety levels. He gives subjects in the first group an extra two cups of coffee a day for six months

The second group receives an extra two cups of decaffeinated coffee a day for the same time period. Importantly, subjects do not know whether they are being given regular or decaffeinated coffee. By providing one group with decaffeinated coffee, Dr. Wilkins is trying to account for which potential element of the experiment?
A) participant fraud
B) inter-rater reliability
C) the placebo effect
D) variability

Answer: C
Rationale: The placebo effect is a measureable and experienced improvement in health or behavior that cannot be attributable to a medication or treatment. In this example, subjects drinking coffee may act more anxious, simply because they expect coffee to make them anxious. Because subjects do not know whether they are receiving regular or decaffeinated coffee, Dr. Wilkins can control for this effect.