Final answer:
A within-subjects design controls for individual differences by having the same participants in all conditions. Random assignment helps distribute lurking variables evenly, allowing researchers to confidently attribute differences in outcomes to the treatments given.
Step-by-step explanation:
When using a within-subjects design in experimental research, pre-existing individual differences among participants are largely controlled for because the same individuals participate in all conditions of the study.
This design is particularly efficient in ensuring that any differences in outcome can be attributed to the independent variable rather than individual differences among participants.
Random assignment plays a crucial role in experimental design by distributing lurking variables evenly and making sure the sole difference in group experience is the treatment administered by the researcher. In this manner, researchers can infer cause and effect relationships between the independent and dependent variables more reliably.