Control groups are mainly used for what purpose in experiments?

Control groups are essential in experiments primarily to minimize external effects, ensuring that the results are due to the treatment being tested rather than other variables. By having a control group that does not receive the experimental treatment, researchers can compare this group with the experimental group to identify if any observed changes are genuinely due to the treatment. This allows for a clearer interpretation of the effects of the independent variable being tested.

For instance, if an experiment is testing the effectiveness of a new drug, the control group might receive a placebo. Any difference in outcomes between the groups can thus be attributed to the drug rather than outside influences or variations that might affect both groups alike. This control helps validate the experiment's findings and supports the conclusion drawn from the data.

The other choices focus on different aspects of experimental design. Observing natural behavior pertains more to observational studies rather than controlled experiments. Measuring response to change refers to assessing the effect of an independent variable, which is a step that occurs after establishing control conditions, rather than the primary role of the control group. Developing hypotheses is a preliminary phase in scientific research, not a purpose of control groups within the experimental design itself.