For example, if a researcher is interested in the effect of a new medication on blood pressure, they could use a within-subjects design by measuring blood pressure in the same group of participants both before and after taking the medication.

Commonly used in everyday life, within-subjects designs can help us understand how individuals respond to different situations. For instance, imagine you’re trying to figure out which type of exercise helps you feel more energized throughout the day. You decide to compare your energy levels after doing yoga and after going for a run.

Within-subjects factors involve comparisons of the same subjects under different conditions. For example, in the "ADHD Treatment" study, each child's performance was measured four times, once after being on each of four drug doses for a week. Therefore, each subject's performance was measured at each of the four levels of the factor "Dose."

Examples A course of Cognitive Decline in Hematopoietic Stem Cell Transplantation: A Within-subjects Design (Friedman et al., 2009). Beliefs, attitudes, and intentions toward nuclear energy before and after Chernobyl in a longitudinal within-subjects design (Verplanken, 1989).

Another common example of a within-subjects design is medical testing, where researchers try to establish whether a drug is effective or whether a placebo effect is in order. The researchers, in the crudest form of the test, will give all of the participants the placebo, for a time, and monitor the results.