control variable

[ kuhn-trohl vair-ee-uh-buhl ]

noun

1. Also control. Statistics. a person, group, event, etc., that is used as a constant and unchanging standard of comparison in scientific experimentation. Compare dependent variable ( def 2 ), independent variable ( def 2 ).
2. (in computer programming) a variable that is used to regulate the flow of control, or order of execution, generally the number of times a loop will execute.

Word History and Origins

Origin of control variable¹

First recorded in 1910–15

Example Sentences

Omitting health status as a control variable increases the estimated hazard ratio to 1.10 (95 percent CI, 1.03–1.19).

From The Daily Beast

More About Control Variable

What is a control variable?

In a scientific experiment, a control variable is a factor that is kept the same for every test or measurement in order to make sure that the results can be compared fairly.

In general, a variable is any factor that can change or be changed. So, for instance, if you’re measuring how effective a medication is, variables could include the amount of dosage, how frequently it’s taken, and the characteristics of each test subject, such as their age and weight. Variables are called variables because they vary, but the point of a control variable is that it doesn’t.

In the context of scientific experiments, there are three different types of variables: dependent variables, independent variables, and control variables. Independent variables are the factors that you change. Dependent variables are things that are affected by the changes that you make—the results of the tests (which depend on the independent variables). Control variables are the factors that you do not change.

For example, let’s say you’re trying to figure out which brand of plant food will help a sunflower grow to the tallest height. The dependent variable is the final height of the sunflower. The independent variable (the factor that you change) is the brand of plant food. There are a number of other factors that could impact the growth of the plant, including things like the amount of sunlight and the amount of water. To allow for a proper comparison of the results, these need to be control variables—they need to need to be controlled, or kept the same. This way, you can have a greater degree of certainty that the final difference in heights (the dependent variable) is due to which food each sunflower received (the independent variable), not differences in sunlight or water.

Control variables are crucial to scientifically sound experiments and studies. A control variable is sometimes simply called a control. Both terms are widely used in science and statistics.

Why are control variables important?

Science is messy. We like to think of experimentation as a simple process of “change one thing and record what happens,” but in reality, every possible subject of study has dozens of different factors that can impact the results. Control variables are a way of keeping some of these factors the same to create a baseline for comparison.

Scientists are trained to be careful when setting all the variables for an experiment. In many experiments, even minor unintended fluctuations in some factor can make the findings inaccurate or misleading. The results of experiments are sometimes later debunked after it has been revealed that variables were not properly controlled, thus skewing the results.

Understanding the importance of control variables will make you more likely to draw sound conclusions and less likely to fall for claims based on faulty science. For example, when examining suspicious statistics or experiment results, a good place to start is to find out whether control variables were used and what they were—and to ask whether there were other factors that could have been controlled but were not. Knowing the variables is crucial to critical thinking.

Did you know ... ?

The concept of a control group, such as in pharmaceutical studies, is similar to a control variable. The control group is a group of subjects who closely resemble the treatment group in many ways but who do not receive the active medication or factor under study and thus serve as a comparison group when treatment results are evaluated.

What are real-life examples of a control variable?

Dependent, independent, and control variables are crucial elements of any experiment, regardless of what is being studied.

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Students experiment with different-material balls (independent variable) and same dropping distance (control variable), to determine height of the bounce (dependent variable). Good work, 6White Science students. @cjhdragons #d26embracethejourney pic.twitter.com/1QBWjD0aQS

— Sarah Edwards, BS, MA (@safetysarah11) October 1, 2019

What other words are related to control variable?

• dependent variable
• independent variable
• experiment
• scientific method
• control group

Quiz yourself!

True or False? 

In an experiment, the control variable is the one that you change.