Essay on Between vs. Within-subjects Designs

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In simplest terms, an experiment that uses only between-subjects factors is said to use a between-subjects design, and an experiment that uses only within-subjects factors is called a within-subjects design. The fundamental hallmark of a between-subjects design is that each participant is assigned to one and only one level of each factor. For instance, participants might be randomly assigned to either receive negative feedback or positive feedback. Feedback is the independent variable, and it has two levels: positive or negative. It is a between-subjects design because each participant only receives one type of feedback. There are two (2) independent groups of participants in the study: one group receives positive feedback and the …show more content…
This is referred to as “error variance” (Erlebacher, 1977). Error variance is the differences between scores that an experimenter cannot explain. In a between-subjects design, error variance is the variability in the scores within each condition. As the scores within each condition become more spread out, error variance increases. As the error variance increases, it becomes harder to detect whether an effect exists; for example, whether the type of feedback influences self-esteem. An inherent consequence of this is that experimenters do what they can to reduce within-condition variability. They are able to do this by: 1) treating every participant within a condition as similarly as possible; and 2) by seeking a homogeneous sample which is a sample of individuals who are very similar to one another. This accomplishes the following: it reduces error variance and the experimenter is better able to get a diverse sample that is more compatible (Erlebacher, 1977). The fundamental hallmark of a within-subjects design is that the same participants are exposed to more than one level of the factor. For instance, if we use the same example as described above, the same participants would receive both the positive and negative feedback and the experimenter would measure

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