Video: Independent Variables in Experiments

Which of the following statements most correctly defines an independent experimental variable? [A] An independent experimental variable is a quantity that does not change in value during an experiment. [B] An independent experimental variable is a quantity that predictably changes in value during an experiment. [C] An independent experimental variable is a quantity that may unpredictably change in value during an experiment. [D] An independent experimental variable is a quantity that cannot change in value.

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Video Transcript

Which of the following statements most correctly defines an independent experimental variable? A) An independent experimental variable is a quantity that does not change in value during an experiment. B) An independent experimental variable is a quantity that predictably changes in value during an experiment. C) An independent experimental variable is a quantity that may unpredictably change in value during an experiment. D) An independent experimental variable is a quantity that cannot change in value.

So, we have these four answer options, and we want to pick which one most correctly defines this term independent experimental variable. Now, when it comes to experiments, there are lots of variable types involved, independent experimental variables, dependent variables, uncontrolled variables, and so on. To understand what this kind of variable is, let’s see what it means in the context of an experiment.

An experiment is simply something we conduct in order to test a prediction that we have. And our prediction can be almost anything about the natural world. Say that we’re on a beach vacation, and we make the prediction that the farther we wade out into the water, the taller the waves we encounter will be. This is a prediction we can run an experiment to test.

Of all the possible variables involved in this experiment, there is one that we want to change on purpose. The variable we want to vary on purpose is the distance we are from the shoreline. It’s by changing that distance that we can test our prediction in this experiment. The distance we’ve walked out from the shoreline, which is the distance we’ve walked into the ocean, is the independent experimental variable. It’s the variable we change deliberately to investigate our prediction.

Knowing this, let’s revisit our four answer options and see which description matches up with what we understand now about independent experimental variables. Option A says that an independent experimental variable is a quantity that does not change in value during an experiment. But we saw in the case of this wave height experiment that it does. In fact, this variable must change in order for us to test our prediction. We won’t choose option A then as our answer.

Option B says that an independent experimental variable is a quantity that predictably changes in value during an experiment. And this sounds much more like what we found earlier. An independent experimental variable does change, but it does so in a predictable way because we’re designing that change. In this case, say, we could walk out into the water in increments of one meter. That could be part of our experimental design, which would mean that this variable, the distance from the shoreline, our independent variable, changes predictably. Option B then is looking good.

We want to choose though the statement that most correctly defines this term, so let’s look at the remaining two. Option C says, an independent experimental variable is a quantity that may unpredictably change in value during an experiment. This notion of changing unpredictably goes against what we understand of experimental design in choosing ways for our independent variable to change. If a variable did change unpredictably, that would be better described by an uncontrolled experimental variable. An independent variable, on the other hand, does change, but it does so predictably. So, we won’t choose option C then.

Option D says that an independent experimental variable is a quantity that cannot change in value. To see how this would work, imagine that, in our beach experiment, we stay in the same place, the same distance from the shore. In that case, we can never move out into the waves to test our prediction. We would just be standing there. So, an independent experimental variable does indeed need to change in order for the experiment to be conducted. Option D then is off the table as well. Like we expected, we choose option B as our answer. An independent experimental variable is a quantity that predictably changes in value during an experiment.

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