Identify the dependent and controlled variables in an investigation.<6d)
Identify a single independent variable in a scientific investigation and explain how this variable can be used to collect information to answer a question about the results of the experiment.<6e)

The same CONTENT TIP applies to Standard 6d and Standard 6e.

Controls and variables are key features of many scientific investigations. For example in studying the transport of water by plants, the investigators may ask the testable question: “How much water will enable the plant to grow the most?” In this situation, the investigators can vary the amount of water that they provide for different containers, each with the same kind of plant in the same kind of situation (size of pot, amount of sunlight, beginning condition of the plant, etc.).

The amount of water is the independent variable. It is the condition of the experiment that the investigator changes from one sample to the other. Some educators recommend emphasizing the “i” in the beginning of “independent,” saying that this is the condition that I change. There needs to be only one independent variable. Otherwise, it will not be clear which one caused the change, or whether the two of them affect each other or not.

The investigators also need to decide what they think will change because of the different amounts of water and how they will measure it. In this case, they may measure the height of the plant. Since the height changes depending on the amount of water, it is called the dependent variable. Note that the investigators could choose to use other measurements such as the number and size of leaves. Assuming these are changing because of the differences in the independent variable, they would also be called dependent variables. In beginning to develop skills with designing experiments and variables, it is best to focus on just one dependent variable.

Since only one condition is being changed by the investigators, everything else needs to be as identical as possible from one sample to another. The amounts and timing of watering should be the same for all plants. All the plants should be of the same type and begin in the same condition (age, size, etc.). The pot size and amount/timing of sunlight should be the same. Since all of these things could vary from one sample to the next, they are called variables. Since the investigators are controlling them so they are as identical as possible from one sample to the next, they are called controlled variables. There should be as many controlled variables as necessary to ensure that the only causative difference comes from changes in the independent variable.