A researcher is conducting an experiment on the effects of caffeine on memory. Participants in the caffeine group are tested in a brightly lit room in the morning, while participants in the control group are tested in a dimly lit room in the afternoon. A colleague points out that any difference in memory performance could be due to the lighting or time of day rather than caffeine.
Which of the following best describes the colleague's concern?
Demand characteristics are influencing participants' responses
The placebo effect is improving performance in the caffeine group
Random assignment has not been used to allocate participants to groups
Confounding variables make it impossible to establish a causal relationship between caffeine and memory
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