A variable is any factor, trait, or condition that exists in differing amounts or types. An experiment usually has three kinds of variables: independent, dependent, and controlled. In a good experiment the scientist must be able to measure the values for each variable.
Independent variable: the condition you change during the experiment. In most good science fair projects only one independent variable is changed at a time.
Dependent variable(s): the variable(s) which you observe during the experiment.
Controlled variable(s): the variable(s) which you try to keep the same during the experiment.
For more information and examples of how to identify variables in a science project check out our variables reference page.
To self-check whether or not you have done a good job identifying and thinking through your project's variables, think about the following questions and answer "yes" or "no" honestly.
If you answered "no" to any of the self-check questions then your project may not be a good one yet. Go back and:
- Figure out how to improve your experimental design to the point that you can honestly answer "yes" to all of the questions.
- If you can't do number 1, you may need to ask your teacher or another adult mentor for help. On rare occasion some of these questions may have a "no" answer even for a very good project. If you think this is the case, be prepared to explain your thinking to your teacher/adult mentor. Otherwise, you may need to consider choosing a different science question for your project.
