Book 26, Question 101
What is a control, and why does a test need one?
A control is a part of a test where you change nothing, so you have something to compare.
Say you think music helps you remember words. You read a list in silence first, which is your control. Then you read a different list of the same length while music plays. Without the control, you would not know if the music did anything. A control makes the answer trustworthy.