Control variable


 * For control variables in mathematics, see independent variable.

Control variables are those variables that are not changed throughout the trials in an experiment because the experimenter is not interested in the effect of that variable being changed for that particular experiment. (In other words, control variables are extraneous factors, possibly affecting the experiment, that are kept constant so as to minimize their effects on the outcome.)

In a scientific experiment, the controlled variable never changes; it is the same for every setup.