Jerrika wants to study the impact of caffeine consumption on performance in a classroom. She takes two classes (one meets at 9 a.m. and the other meets at 3 p.m.) and provides caffeine to the 9 a.m. class. She then compares scores on identical exams
between the two classes. She finds that caffeine dramatically affects performance by improving scores. What might be a concern about the conclusions she draws about her data?
a. Assignment to the experimental versus control groups was not random.
b. There may have been a placebo effect.
c. The conclusions would be stronger if she had varied the exams between the two classes as well.
d. Jerrika cannot compare scores on identical exams.
Answer: A
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