2.3. Between-Subjects Versus Within-Subjects

If the goal is to compare two or more Web sites or design alternatives, you'll face the question of whether to test these between-subjects or within-subjects. “Between-subjects” means that each participant receives one version or another during the session, but not more than one. “Within-subjects” means that each participant will receive all or some of the versions being tested during their session.

In the simplest sense, a between-subjects design is the cleanest way to test different versions of something. If each participant interacts with only one version, doing all of the same tasks, and being asked all of the same questions as participants on other versions, then any statistically significant ...

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