VARIABLES
You must take time to identify your variables BEFORE you develop your procedure. A variable is something that CAN change or BE changed. There are three kinds of variables:
Independent
Dependent
Controlled
INDEPENDENT VARIABLE
In a well designed experiment, there should only be ONE variable that is changed on purpose. This is called your INDEPENDENT VARIABLE.
Remember our sample question: Does soaking bean seeds before planting affect how fast they will grow?
In this example, the thing we are changing on purpose is soaking the seeds before planting them. So the independent variable is soaking the seeds. We should have two sets of seeds in our experiment, one set will be soaked, one set will not be soaked. We are deliberately changing our independent variable to see how it affects plant growth.
DEPENDENT VARIABLE
We call what what we think will change in our experiment our DEPENDENT VARIABLE. In our example, we think that the growth of the plant will DEPEND on whether we soak the seeds or not. So our dependent variable is growth.
CONTROLLED VARIABLES
We must try to keep all other things that might affect the growth of the bean seeds exactly the same for our two sets of seeds. These might include:
Type of bean
Amount of water and sunlight the beans get
Type of soil used
Type of container used
I want to keep all these the same so I can determine if soaking, and ONLY soaking, causes
any differences in how the plants grow. I control these variables by keeping them the same,
so these are my CONTROLLED variables.