Why is a control group essential in experimental research?

• A. A control group provides a baseline to determine whether observed effects are due to the manipulation rather than extraneous factors.
• B. A control group increases the sample size.
• C. A control group allows measurement of reliability.
• D. A control group eliminates the need for random assignment.

Answer: (A)

A control group provides a baseline for comparison, allowing researchers to determine whether observed effects are due to the manipulation rather than extraneous factors. By keeping everything else the same between the control and experimental groups, any difference in the dependent variable can be attributed to the independent variable. This helps establish cause-and-effect and guards against confounding influences like placebo effects, natural variation, or measurement error. If there were no control group, it would be hard to tell whether outcomes came from the manipulation or from other uncontrolled factors.

The other options don’t capture this essential role. A control group doesn’t automatically increase the number of participants or the study’s power; sample size is about how many people you recruit and how you design the study. Reliability refers to the consistency of measurement, not to the function of a control group. And even with a control group, random assignment is still important to ensure the groups are comparable at the start; it doesn’t replace the need for a control group.