Random assignment of participants to conditions and experimental control of extraneous variables allows researchers to infer internal validity.

Random assignment and experimental control are both important methods for ensuring internal validity in research studies. Random assignment helps to distribute extraneous variables evenly across experimental groups, reducing the likelihood that any one group will be systematically different from the others. Experimental control involves systematically manipulating independent variables while holding all other variables constant, which ensures that any observed effects are due to the manipulation rather than other factors. Together, these methods help researchers draw valid conclusions about cause-and-effect relationships between variables.