5. in the study, neither the subjects nor the experimenters interviewing the
subjects knew if the subject was receiving the caffeine pills or the caffeine-
free pills. why might this be an important design element in the study?

To remove the bias

Step-by-step explanation:

The study in which neither the subject nor the experimenter knows which subject is receiving a particular treatment is known as double blind study.

In the given study, the treatment is caffeine pills. So neither the subjects know they received caffeine pills nor the experimenter knows that which subject received which pill. Hence, this is a double blind study.

Such a study is used to remove the potential bias from the study. For example, if a subject is told that he is given a caffeine pill his actions will re-enforce that he has taken the pill, even in the case when he is given a placebo instead of actual pill. So the belief of the subject may cause bias in the result. This is removed by using the double blind study.

Also, since the experimenter also does not know which subject received the treatment, they won't act in different ways towards different subjects to give away any hints or clue. If the experimenter knows which subjects is given actual treatment, he may behave differently with him. So the double blind study removes this sort of bias as we..

the square root of 16 is 4.

4*4 = 16