Answer is controlled experiment.
An experiment in which all the variables are same or constant except for one variable is called controlled experiment. In this type of experiment a set of data is considered for a control group and one or more other groups are examined. All conditions are identical to the control group and each other except one variable.
Example of a controlled experiment:
How the type of soil affects the time of seed germination?
To address this question, a controlled experiment is set up. For the experiment four identical pots were taken and filled each with a different type of soil. Bean seeds were planted in each pot, place the pots in a sunny window, water them, and measured how long it takes for the seeds in each pot to germinate.
This is a controlled experiment because the aim was to keep every variable constant except the type of soil used.
