Variables and Operational Definition

Everyone should be working on the rough drafts for you variables and your operational definition. All rough drafts should be hand written in the "Rough Draft" section of your folder.

The variables you should have are the independent, dependent, control, and constants. Remember, not all experiments have a control. The independent variable is also called the manipulated variable. This is the variable that you are changing for your experiment or the thing you are testing. When you wrote your purpose "The purpose of this experiment is to determine how ___________ affects ____________." The independent variable would be in that first blank. The dependent variable is also called the responding variable. This is the thing that changes because of what you did in the experiment or the second blank "affects ______________." The control is the thing you are NOT testing on or what you can use to compare your results to. Not every experiment has a control. You will have several constant variables in your experiment. These are all of the things that you will keep the same (if you change to many things at once, we won't know what actually caused your results).

The operational definition describes exactly how and what you are measuring. You need to be specific about what is being measured, so other people could repeat your experiment as you did it. This is where you decide what you mean by your independent and dependent variables. For example, what do you mean by most effective, plant growth, how high, how accurate, etc.

One of the examples in your instructional packet is "How does the amount of time studying affect science grades?"

Variables:

• Independent: amount of time studying
• Dependent: science grades
• Constant: method of study; study environment; student tested; type of assignment; (can you think of more?)
• Control: initial grade (or maybe you have another in mind?)

Operational Definition: In this experiment "amount of time studying" will be defined as how many minutes per night a student spends reviewing material, doing practice questions, or quizzing themselves. "Grade" will be defined as the student's overall percentage in science class.

Now, for the operational definition, there could be more than one way to test this. Perhaps some people would say we should look at test scores only. Someone else might say studying is any time spent doing any science work. This is why it is important to describe exactly what will be measured in this experiment. Units should be included too. Do not describe the method of measurement, just the what!