Science, Tech, Math › Science Scientific Variable Share Flipboard Email Print Science Chemistry Scientific Method Basics Chemical Laws Molecules Periodic Table Projects & Experiments Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 14, 2020 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 that 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 that are controlled or held constant throughout an investigation. They 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 though 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.