Because if you change more than one variable at a time, you can't tell which is affecting the results.
If you test only one variable then you know that the difference in the experimental and control setup is that one independent variable. If you test more than one you will not know which one made the difference.
Independent variable : )
This variable is chosen by the research team according to the experiment project.
The independent variable.
It's called a 'fair test'
The independent variable.
A variable test?
it is a fair test
this is an experiment that only one varible is manipulated at a time
It would not be a fair test if there were 2 or 3
Manipulated variable
Manipulated variable