[Page 471]Research often involves comparing two or more conditions on one or more dependent variables. In this case, researchers must choose between two major categories of research design: (1) between-subjects designs (also called independent groups) and (2) within-subjects designs. This choice will determine whether each condition will be administered to a separate group of participants or whether each condition will be administered to all participants. In a between-subjects research design, a participant experiences only one condition; as such, a comparison of conditions means comparing different groups of people.

For example, consider an experiment examining the effect of mindfulness meditation on symptoms of anxiety. To implement a between-subjects research design, researchers would recruit a group of people experiencing symptoms and then randomly assign them either to the ...