Why is a control group used in an experiment?

• A. To provide a baseline for comparison and to isolate the effect of the independent variable.
• B. To prove the experiment is ethical.
• C. To eliminate the need for randomization.
• D. To speed up data collection.

Answer: (A)

The main idea is that a control group provides a baseline for comparison and helps isolate the effect of the variable you’re testing. In an experiment, you want to know whether changing the independent variable actually causes a change in the dependent variable. The control group experiences all the same conditions as the experimental group except for the manipulation of the independent variable, so any differences you observe can be attributed to that manipulation rather than to other factors.

For example, if you’re testing a new fertilizer on plant growth, keep everything else identical for both groups—sunlight, water, soil type—while only the experimental group receives the new fertilizer. If that group grows more than the control group, you can infer that the fertilizer is contributing to the increased growth, not random variation or environment.

This setup also helps account for placebo effects or other unintended influences, ensuring the result reflects the treatment itself. It’s not about ethics, and randomization or faster data collection are separate considerations that support good experimental design.