What Is an Independent Variable?

What Is an Independent Variable in a Scientific Experiment

The independent variable is the one you control or change in an experiment.
The independent variable is the one you control or change in an experiment. Hero Images / Getty Images

An independent variable is a variable that doesn't depend on another variable and isn't changed by any factors an experimenter is trying to measure. It's the variable that is controlled or changed in a scientific experiment to test its effect on the dependent variable. The independent variable is denoted by the letter x in an experiment or graph.

Independent Variable Example

For example, a scientist is testing the effect of light and dark on the behavior of moths by turning a light on and off.

The independent variable is the amount of light and the moth's reaction is the dependent variable.

For another example, say you are measuring whether amount of sleep affects test scores. The hours of sleep would be the independent variable while the test scores would be dependent variable.

A change in the independent variable directly causes a change in the dependent variable. If you have a hypothesis written such that you're looking at whether x affects y, the x is always the independent variable and the y is the dependent variable.

Graphing the Independent Variable

If the dependent and independent variables are plotted on a graph, the x-axis would be the independent variable and the y-axis would be the dependent variable. You can remember this using the DRY MIX acronym, where DRY means dependent or responsive variable is on the y-axis, while MIX means the manipulated or independent variable is on the x-axis

More About Variables

The independent variable is only one of the variables in an experiment. Learn about other variables and how they are used to design an experiment.

What Is a Variable in Science?
What Is a Dependent Variable?
What Is a Control Group?
What Is an Experimental Group?