Does Vitamin C make people feel better when they have a cold? A sample of 90 individuals suffering from a cold are recruited to take part in a study. Half of the sample (n=45) is randomly assigned to take Vitamin C for five days, and the other half of the sample (n=45) is randomly assigned to take a sugar pill for five days. At the end of the five-day period, 35 of the individuals who took Vitamin C claimed to feel better, and 20 of the individuals who took the sugar pill claimed to feel better. When asked to explain why several individuals who took the sugar pill claimed to feel better, the researcher said "they likely said they felt better because they received a pill that they believed would make them feel better." We call what the researcher is describing a A. double-blind effect. B. butterfly effect. C. significant effect. D. placebo effect. E domino effect.