Biology: Independent vs. Dependent Variables
"Independent variable" and "dependent variable" are important terms related to controlled experiments. Remember, a controlled experiment is a scientific test in which all conditions are kept constant except for the variable you're testing. The independent variable is the thing you're testing in an experiment. it's often abbreviated as "IV" and sometimes called the "manipulated variable" because you change or manipulate this variable.
In an experiment, the dependent variable is the thing you're observing and measuring the thing you're anticipating may be affected as a result of exposure to the independent variable. It's often abbreviated as "DV" and sometimes called the "responding variable" because it responds to the change that you make. Let's look at a few examples.
Suppose your hypothesis is that if students study 15 minutes a night then they will have higher test grades than those who don't study at all. What's being changed, or manipulated? It's whether or not the student study for 15 minutes. And what's going to be observed or measured in this experiment? What do you think might be different as a result of this increased study time?
You're expecting test grades will be affected. In this experiment, the independent variable is the study time. And the dependent variable – the thing you're measuring or going to observe – is the test grades. Here's another example – see if you can figure it out. This time the hypothesis is that if people who have headaches take aspirin, then they will get relief faster than those who who don't take aspirin for headaches.
So, what's the thing that's different in this case? The thing that's different – the independent variable – is whether or not somebody is taking an aspirin. Then, what are you going to measure? Your measuring how long it takes for their headache to go away. That's the dependent variable. Here's a final example to help you understand these terms.
You predict that if a brand-name light bulb is left on continuously, then it will burn longer than a bargain brand light bulb used in the same manner. In this case, what is the independent variable? It’s the brand name light bulb. What are you measuring? You're measuring how many hours the light bulbs work before burning out,
Which is the dependent variable. The independent variable is the brand name light bulb, and the dependent variable is the amount of time the light bulbs work before burning out. So to review, the independent variable is the thing that you're testing sometimes this is referred to as the cause in an experiment.
It is also the "if" part of your hypothesis. The dependent variable the thing you're measuring is the effect. It is also the "then" part of your hypothesis.