In experimental design, what is the primary role of a control group?

• A. A control provides a baseline for comparison and isolates the effect of the independent variable.
• B. A control is unnecessary in well-designed experiments.
• C. A control introduces additional variables.
• D. A control applies the independent variable to all groups.

Answer: (B)

The key idea here is that experiments need a reference point to tell whether changing the variable actually causes a change. A control group provides that reference by matching the experimental group in every way except for the factor you’re testing. Because conditions are held constant, any difference in outcome can be attributed to the independent variable rather than other factors or random variation. This baseline lets you isolate the effect of the manipulation and rule out confounding influences. For example, in testing a drug, the control group might receive a placebo; both groups are treated the same otherwise, so if the drug group shows a different response, you can attribute it to the drug itself. The control does not add extra variables, and you don’t apply the independent variable to all groups, since that would remove the comparison that a control provides. Controls are essential to meaningful conclusions, not optional.