What is a controlled experiment?

What is a controlled experiment?

• A. An experiment in which all conditions except one are held constant.
• B. An experiment with multiple uncontrolled variables.
• C. An experiment without a hypothesis.
• D. An experiment where the outcome is predetermined.

Answer: (A)

In a controlled experiment, you isolate the effect of a single factor by keeping all other variables fixed. This lets you attribute any observed change in the outcome to the factor you intentionally altered—the independent variable—since everything else remains the same. For example, changing the amount of fertilizer while keeping light, water, soil, and temperature constant shows fertilizer’s direct effect on plant growth. If many variables were allowed to vary, you wouldn’t be able to tell which factor caused the difference. The other described scenarios—uncontrolled variables, no guiding hypothesis, or predetermined outcomes—do not describe the careful control needed to isolate a cause-and-effect relationship.

In a controlled experiment, you isolate the effect of a single factor by keeping all other variables fixed. This lets you attribute any observed change in the outcome to the factor you intentionally altered—the independent variable—since everything else remains the same. For example, changing the amount of fertilizer while keeping light, water, soil, and temperature constant shows fertilizer’s direct effect on plant growth. If many variables were allowed to vary, you wouldn’t be able to tell which factor caused the difference. The other described scenarios—uncontrolled variables, no guiding hypothesis, or predetermined outcomes—do not describe the careful control needed to isolate a cause-and-effect relationship.