Independent variables are those whose values are controlled or selected by the experimenter.

Dependent variables are those that change based on the independent variables.

One way I remember the difference is that the outcome (dependent variable) DEPENDS on the INput (independent variable).

A control variable is a factor that is held constant so that it won’t affect the impact that the independent variable makes.

Here is an example of a simple experiment. Let’s say we want to test if a basketball bounces higher than a tennis ball when it is dropped.

The independent variable is the type of ball.

The dependent variable is the height of the bounce.

We might test this by dropping balls off of a balcony onto the driveway. To check to see if a basketball bounces higher than a tennis ball, we need to control for certain variables.

We will want to control for the height from which they are dropped. (if one ball falls 10 feet and another 11, how do your really know it is the ball type that made the difference in the bounce?

We also want to control the surface that the balls land on. (eg Make sure both land on concrete as opposed to one landing on dirt or black top or wood.) You also may want to control for things like temperature and weather (would wind or rain affect a bounce?).

The easiest way to control for all of these factors would be to drop both balls at the same time from the same balcony, side by side.

To repeat, the ball type is the input and factor that is purposely varied. The height of the bounce is the dependent variable. It may be affected by the type of ball.

Height, speed, surface, weather, etc are control variables.

– independant variable is the thing that you change in your experiment so the thing you are investigating

– dependant is the thing you measure so the results which you record in your experiment