An example of a(n) is one in which an experiment was conducted on caffeine-induced stress in which neither the class researchers nor the participants in the experiment knew who did and did not receive caffeine until after the study was completed.

The answer is double-blind study.

Explanation:

In a double-blind study, neither the researchers nor the participants are aware about which group is receiving the treatment. This type of study is especially useful to avoid biased reports, likely due to placebo effects; on the other hand, it also prevents researches from accidentally revealing information about the experiment.

political parties perform an important task in government. they bring people together to achieve control of the government, develop policies favorable to their interests or the groups that support them, and organize and persuade voters to elect their candidates to office.

explanation: