within-subject

A within-subject design is one where the same person does every condition — so the comparison lives inside one learner, not across two groups, and each person serves as their own control.

The strength is control: the noise that varies between people (talent, history, mood) cancels in the subtraction, because the same learner does both tasks and the difference is what matters, not the absolute level. The weakness is order: doing one condition first may change what happens in the second (practice, fatigue, carryover), so the conditions must be counterbalanced — half the learners do them in one order, half in the reverse. The free-choice paradigm's gap diagnostic uses within-subject design: the same learner does two unrewarded tasks, and the gap between willingness and persistence is measured per learner, then the gap differences are compared across tasks — the control lives in the subtraction, not in a separate group.