Which design allows individual scores in one condition to be directly paired with scores in another condition (within-subjects design)?

• A. Related design (within-subjects)
• B. Unrelated design (between-groups)
• C. Matched pairs design
• D. Between-subjects design

Answer: (A)

Within-subjects design uses the same participants across all conditions, so you can pair each person's score in one condition directly with their score in the other. This direct pairing controls for individual differences and reduces unexplained variability, making comparisons more powerful. If you have different participants in each condition (between-subjects), you can’t pair scores person-to-person. A matched pairs approach ties participants in the two conditions by matching on characteristics but still involves different individuals in each condition, so you don’t get the same direct one-to-one pairing of scores from the exact same person. Hence, the design that allows direct pairing of scores across conditions is the within-subjects (related) design.