Video: Dependent Variables in Experiments

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

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Video Transcript

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

Alright, we have these four possibilities for the most correct definition of the term dependent experimental variable. To see just what this term means, it’s helpful to understand it in the context of an experiment. An experiment, recall, is something we do to test a prediction. Typically, an experiment involves changing one thing, one variable, and seeing the impact that has on another variable.

As an example of this, say that we’re looking at some trees. And based on our initial observation, we make a prediction. We predict that the taller a tree is, the more leaves it has on it. This is a prediction we can test using an experiment. The experiment will involve measuring the heights of various trees and then counting the leaves on those trees and seeing if our prediction was correct. There are a number of variables in this experiment. But the two that we’re most interested in are the height of the trees and the number of leaves on the tree. And based on our prediction, that the taller a tree is, the more leaves it will have, we can say that, in this experiment, the number of leaves on the trees is a dependent variable. It depends, according to our prediction, on the height of the tree.

In the language of experimental design, the height of the trees in this case is the independent experimental variable. And then, as that height varies, we expect, by our prediction, that the number of leaves on the trees will vary too. We call this the dependent experimental variable. So we go along measuring the heights of trees, that’s the independent variable, and counting the number of leaves they have. That’s the dependent variable. True to its name then, we expect our dependent experimental variable to depend on our independent variable. In other words, as the independent variable changes, we expect our dependent variable may change too. Knowing that, let’s revisit our four answer options.

Option A says that a dependent experimental variable is a quantity that may change in value during an experiment when an independent variable changes in value. This is a great description of what we found as we considered our tree height-leaf count experiment. When the independent variable is changed, the dependent variable may well change too. Option A is looking promising. Let’s continue on the other choices. Option B says that a dependent experimental variable is a quantity that does not change in value during an experiment. But if we consider our tree experiment, we can see that this is unlikely to be true. Even if our prediction, that taller trees means more leaves, isn’t exactly correct. It’s likely that the dependent variable in this case, the number of leaves, will change from tree to tree. And in general, we do expect a dependent experimental variable to change. So we won’t choose option B as our answer.

Option C says that a dependent experimental variable is a quantity that predictably changes in value during an experiment. But this is actually a better description of the independent experimental variable. That’s the variable in an experiment that we change in a deliberate, predicted way. And it’s in response to this plan to change that a dependent experimental variable may or may not change. In either case, if it does change, we can’t predict how that will happen. This option then isn’t our best definition either.

Option D says that a dependent experimental variable is a quantity that may unpredictably change in value during an experiment. It’s true that a dependent variable may change in a way that we can’t predict ahead of time. Strictly speaking, option D is not incorrect. But remember, we want to choose which statement most correctly defines this term. And option D, though it’s correct in saying the dependent experimental variable may unpredictably change during an experiment, leaves out the connection between the dependent experimental variable and the independent variable. This connection is important because as the experiment commences, we may discover that the changes in the dependent variable are unpredictable but in fact can be predicted from the changes in the independent variable. That’s something we would find out as we go along.

So better than the definition offered by option D is the one offered by option A. This choice ties the changes that may occur in a dependent experimental variable to changes in an independent variable. For that reason, it’s the most correct definition here of a dependent experimental variable.

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