It's really an opinion question from your perspective of terrorism.
Answer: use tentative phrasing. be reasonably sure you are correct. be sure your motive for offering an analysis is truly to help
Explanation:
The variable is the group that was given caffine, because thats what the doctors manipulated. They possibly altered the natural memory of the participants by giving them caffine. A more specific variable could be how much caffine each participant is given and what time are they given it.
