In a matched pairs design, how are participants allocated to conditions?

• A. One participant in a pair is assigned to the control condition and the other to the experimental condition
• B. Both participants in a pair receive the same condition
• C. Pairing is used but assignment is random with no pairing
• D. Participants are assigned to conditions without any pairing

Answer: (A)

Matched pairs design pairs participants who are similar on a relevant characteristic, and then assigns one member of each pair to the experimental condition and the other to the control condition. This inside-pair assignment controls for differences between individuals because each pair serves as its own mini-comparison, reducing unrelated variability and increasing sensitivity to detect treatment effects.

If both members of a pair received the same condition, there would be no direct within-pair comparison, which defeats the purpose of the design. Pairing without assigning one to each condition wouldn’t implement the critical cross-condition contrast, and allocating participants to conditions without pairing misses the advantage of controlling for individual differences through the paired structure.