What research design randomly assigns participants to different groups?

The independent groups design involves randomly assigning participants to different groups, which helps ensure that each group is comparable and can effectively reduce the impact of confounding variables. This randomness allows for a more straightforward comparison of the effects of the independent variable on each group, enhancing the internal validity of the experiment.

In contrast, matched groups design specifically pairs participants based on certain characteristics before assigning them to groups, which does not involve random assignment in the same way. Within-subjects and repeated measures designs involve the same participants across different conditions, which inherently means that they do not involve random assignment to separate groups but rather focus on repeated observations of the same individuals. Thus, the independent groups design stands out for its use of random assignment, making it an essential structure in experimental research.