In experimental design, how do the control and experimental groups differ?

• A. The control group does not receive the experimental treatment, while the experimental group does.
• B. The control group is used for measuring the dependent variable; the experimental group is used as the baseline.
• C. The control group uses different measurement instruments.
• D. The control group is always larger than the experimental group.

Answer: (D)

The main idea is that the control and experimental groups are treated differently only in whether they receive the experimental treatment. The control group does not get the treatment (it may receive no treatment or a placebo), while the experimental group receives it. This difference lets you compare outcomes and attribute any changes in the dependent variable to the treatment itself, rather than to other factors. The same procedures and measurement tools should be used for both groups to keep the comparison fair and valid, so the results reflect the effect of the independent variable. Group sizes aren’t defined as one always being larger; researchers choose sizes based on statistical power and practical considerations, and equal-sized groups are common but not mandatory.