Final answer:
Dr. Kim's knowledge of who is in which group could introduce experimenter bias into the experiment's results. A double-blind study would be the most suitable method to avoid such biases and validate the effects of caffeine on alertness objectively.
Step-by-step explanation:
If Dr. Kim knows who is in which group in the experiment and expects the caffeinated coffee group to be more alert, this may introduce experimenter bias and affect the results. Experimenter bias occurs when a researcher's expectations influence the outcomes of a study. For instance, Dr. Kim might unconsciously rate the alertness of participants drinking caffeinated coffee higher due to her expectations. To minimize this effect, it is essential to conduct a double-blind study, where neither the participants nor the researchers know who belongs to the control or experimental groups. This method reduces the influence of both experimenter and participant expectations that can lead to a placebo effect, where simply expecting a change can cause that change to happen.
In well-designed research, random assignment and control groups are used to eliminate confounding variables, ensuring that the only difference between the treatment groups is the one imposed by the researcher. This means that if the groups respond differently, the difference can be attributed to the effect of the substance being tested, in this case, caffeine.