What is a control variable in an experiment?

What is a control variable in an experiment?

• A. The variable that is measured.
• B. The variable that is deliberately changed.
• C. The variables that are kept constant to ensure results are due to the independent variable.
• D. The variable that is the outcome.

Answer: (C)

The key idea is that some factors in an experiment are kept constant to ensure any observed effect comes from what you deliberately change. These constant factors are the control variables. By holding them steady, you rule out alternative explanations and make it clearer whether changes in the outcome are truly due to the independent variable, the factor you purposefully manipulate. For example, if you’re testing how different amounts of fertilizer affect plant growth, you would keep sunlight, water, soil type, pot size, and other conditions the same for every plant. Those stable factors are control variables. Understanding the other terms helps: the variable you measure is the outcome or dependent variable—it tells you what happened but isn’t kept constant. The variable you actively change is the independent variable. The control variable sits in the middle, staying constant to ensure the results reflect the effect of the independent variable.

The key idea is that some factors in an experiment are kept constant to ensure any observed effect comes from what you deliberately change. These constant factors are the control variables. By holding them steady, you rule out alternative explanations and make it clearer whether changes in the outcome are truly due to the independent variable, the factor you purposefully manipulate.

For example, if you’re testing how different amounts of fertilizer affect plant growth, you would keep sunlight, water, soil type, pot size, and other conditions the same for every plant. Those stable factors are control variables.

Understanding the other terms helps: the variable you measure is the outcome or dependent variable—it tells you what happened but isn’t kept constant. The variable you actively change is the independent variable. The control variable sits in the middle, staying constant to ensure the results reflect the effect of the independent variable.