What is the purpose of using controlled variables in an experiment?

• A. To keep some factors constant so that observed effects are due to the manipulated variable.
• B. To randomly change all factors during testing.
• C. To increase the variability of the results.
• D. To speed up data collection.

Answer: (A)

Controlling variables means keeping factors that could influence the outcome the same across all experimental conditions so that any difference you observe can be attributed to the variable you deliberately change. By holding these other factors constant, you isolate the effect of the manipulated variable. For example, in testing how different light levels affect plant growth, you would keep water, soil type, temperature, and pot size constant. If these other factors varied, changes in growth could be due to watering or temperature instead of light, making the results ambiguous. This approach is key for establishing a cause-and-effect relationship.

Randomly changing all factors would introduce uncontrolled variation and blur which factor is responsible for any change. Increasing variability of results makes it harder to draw conclusions. Speeding up data collection isn’t the goal, since accurate, reliable measurements require consistent conditions.