A researcher wants to determine if a new herbal tea improves concentration. One group of participants drinks the new tea before taking a concentration test. A second group of participants is simply asked to take the same concentration test without drinking any tea. The researcher finds that the tea-drinking group scored higher. Why is it difficult to conclude that the herbal tea was the true cause of the improved performance?

A researcher wants to test if a new energy drink improves reaction time. They have one group of participants drink the new energy drink and then complete a reaction time test. A second group of participants drinks nothing and then completes the same test. The researcher finds that the energy drink group has a faster average reaction time. Why is the group that drank nothing an inadequate comparison group for this experiment?

In an experimental design, the ____ group consists of participants who do not receive the experimental manipulation and serves as a baseline for comparison.