What is the purpose of a control group in experimental design?

• A. To demonstrate what happens when a treatment is applied
• B. To demonstrate what happens without a treatment by comparing to a baseline
• C. To confuse the outcome
• D. To expedite the experiment

Answer: (B)

Having a baseline for comparison is essential. A control group shows what happens when the independent variable is not applied, under the same conditions as the treated group. This sets a reference point so that any difference observed can be attributed to the treatment rather than random variation or other factors. By comparing the outcomes between groups, you can determine the actual effect of the treatment and rule out alternative explanations. Sometimes the control receives no treatment or a standard/sham treatment to keep conditions identical and reduce bias. This is why the purpose is to demonstrate what happens without a treatment by comparing to a baseline. The other options describe what happens to the treated group, not the role of the control, or are not goals of experimental design.