What Is a Scientific Variable?

Understand Key Variables in an Experiment

Scientific variables are important for the scientific method. (Getty Images)

A variable is any factor that can be changed or controlled. In math, a variable is a quantity that can assume any value from a set of values. A scientific variable is a little more complicated, plus there are different types of scientific variables.

Scientific variables are associated with the scientific method. Variables are things which are controlled and measured as part of a scientific experiment. There are three main types of variables:

Controlled Variables

As the name implies, controlled variables are factors which are controlled or held constant throughout an investigation. The are kept unchanging so that they won't influence the outcome of the experiment by changing. However, they do have an impact on the experiment. For example, if you are measuring whether plants grow better when watered with milk or water, one of the controlled variables might be the amount of light that is given to the plants. Even through the value may be held constant throughout the experiment, it is important to note the condition of this variable. You would expect the growth of the plant might be different in sunlight as compared with darkness, right? Tracking controlled variables makes it easier to replicate an experiment. Sometimes the effect of a variable comes as a surprise, leading to a new experiment.

Independent Variable

The independent variable is the one factor that you purposely change in an experiment. For example, in an experiment looking at whether plant growth is affected by watering with water or milk the independent variable is the substance used to water the plants. Many experiments are based on an "if-then" scenario, where the researcher measures what happens if a variable is changed. The "if" part of the experiment is the independent variable.

Dependent Variable

The dependent variable is the variable that you are measuring in order to determine whether or not it is affected by a change in the independent variable. In the plant experiment, the growth of the plant is the dependent variable. In an "if-then" experiment, the response to a change refers to the dependent variable. Its value depends on the status of the independent variable.

Plotting a Graph of Variables

When you plot a graph of your data, the x-axis is the independent variable and the y-axis is the dependent variable. In our example, the height of the plant would be recorded on the y-axis while the substance used to water the plants would be recorded on the x-axis. In this case, a bar graph would be an appropriate way to present the data.

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