What is a control group in an experiment?

• A. The baseline group that does not receive the experimental treatment.
• B. The group that receives the experimental treatment.
• C. The group used to calibrate instruments.
• D. The group observed only after the experiment.

Answer: (A)

In experiments, you need a baseline to see what happens without the treatment. The control group serves as that baseline: they are treated the same as the experimental group in every way except they do not receive the experimental treatment. This setup lets you attribute any difference in outcomes to the treatment itself, rather than to chance, time, or other variables.

Why this matters: comparing the control group to the group that gets the treatment shows whether the treatment actually caused a change, which is the core goal of an experimental design.

The other options don’t fit as a control group: the group that receives the experimental treatment shows the effect you’re testing for, not a baseline for comparison; the group used to calibrate instruments is about measurement accuracy, not a comparison of outcomes; and a group observed only after the experiment lacks pre-treatment data to establish a true baseline.