What is the key benefit of a repeated measures design?

In a repeated measures design, the same participants are used across all conditions of an experiment. This design's key benefit is that it controls for individual differences among participants, effectively ensuring that subject variables remain constant across conditions. By having the same individuals participate in each condition, any variability due to differences in participant characteristics (such as age, gender, or background) is minimized. This allows researchers to attribute differences in outcomes more confidently to the experimental manipulation rather than to pre-existing differences among participants.

In contrast, repeated measures designs do experience challenges, such as potential carryover or order effects where the sequence in which conditions are presented could influence outcomes. While repeated measures designs can enhance statistical power, they do not inherently increase sample size requirements; on the contrary, they often allow researchers to conduct studies with fewer participants. Therefore, option C is aligned with the primary advantage of this methodological approach.