How many variables in a scientific experiment should we test

How many variables in a scientific experiment should we test at one time and why?

Solution

At a time, only one variable must be tested in an experiment. This variable is usually referred to as the test variable and it is an independent variable, meaning it does not show any change due to change in other factors or variables involved in the experiment.

Variables in an experiment can be classified as independent, dependent and controlled. The quantities of the independent variable are changed to study its effect on the dependent factors.

If, in an experiment you have two or more independent variables and you choose to change the quantities of both or all of them, without testing each one independently, then you will not know which of the independent variables has brought about a change in the dependent factor.

It can also be that the change in the dependent variable is due to the synergistic or antagonistic effect of the independent variables. But since you have taken both at the same time, without individually testing each one priorly, there is no way you can conclude.

So, at a given time only one variable is tested.