Emilio's teacher told his class that a controlled experiment's results are valid only if one factor in the experiment is changed and all the other factors remain constant. Why is this statement true?
A.
Changing several different factors in an experiment takes too much time.
B.
Changing several different factors in an experiment takes too many controls.
C.
When only one factor is changed, you can be more certain that it caused the results.
D.
When only one factor is changed, you don't need to use a control.

Question

Emilio's teacher told his class that a controlled experiment's results are valid only if one factor in the experiment is changed and all the other factors remain constant. Why is this statement true?
 A. 
Changing several different factors in an experiment takes too much time.
 B. 
Changing several different factors in an experiment takes too many controls.
 C. 
When only one factor is changed, you can be more certain that it caused the results.
 D. 
When only one factor is changed, you don't need to use a control.

Vocaloid · Answer

I’ll try to explain with an example:

If I want to know the effect of sleep on my grades, I would only want to change the number of hours of sleep I get. If I also change what I eat for breakfast, then I don’t know whether changing sleep, or changing my breakfast, affects my grades.

With that example, can you try to deduce what the answer is?