Variables: Independent, Dependent, Controlled


Types of Variables in a Science Fair Project

Independent Variable- Amount of Light; Dependent Variable- Plant Growth; Controlled Variables- temperature, humidity, container, soil

Independent variables
Dependent variables
Controlled variables

variable is part of an experiment that can change, such as amount of light, temperature, humidity, time changes, or plant growth.

Independent Variable

In an experiment, an independent variable is a variable that either changes on its own, or you purposely change it.

For example: If the purpose of an experiment is to determine how changes in the amount of light on a plant affects the plant’s growth.

How Plants Grow In Response to Light

The Independent Variable is the the amount of light the plant received.

Ideas for how to change the amount of light.

1. Use sunlight which changes during the day as well as from one day to the next.  You can also use direct and indirect sunlight.

2. If you use artificial light you can determine when and for how long the plant will receive this light. You also have the option to control the wattage of light used–its color–type (fluorescent, UV, incandescent). Just use the same type of light for each test plant–see controlled variables below.

Dependent Variable

The purpose of  changing an independent variable is to determine how the changes affects something else, which is called the dependent variable. In other words, changes in the independent variable may cause the dependent variable to change.

In an experiment, a dependent variable may change due to the changes made in the independent variable.

For the previous plant experiment, “How Plants Grow In Response to Light,”  the growth of the plant is the dependent variable being observed  The plant growth is in response to changes in the amount of light the plant receives, is the independent variable.

Controlled Variables

Controlled variables sounds like an oxymoron. Just remember that variables are things that CAN change. This means that they can be controlled and prevented from changed.

It is important that when you experiment that you have only two variables that change:

1. the independent variable that you want to change and can measure how it changes.

2. the dependent variable that you are measuring to see how much it changes in response to the independent variable.

Changes in any other variable could affect your results.  So, you must try to control any other variable,  meaning you want to eliminate them or control them so that the things being tested are not affected.

For example, in the previous experiment, “How Plants Grow In Response to Light,” the  variables that must be controlled include, the type of plant tested, container, type of soil, temperature, amount of water, humidity, type of light, etc…needs to be the same for every plant tested. Some variable are difficult to control, but you should try to make every effort to keep them the same during the testing.