Within-Subjects Design: Definition and Examples

A within-subjects design, also known as a repeated measures design, is a type of experimental design in which all participants are exposed to every treatment or condition being studied.

Advantages and Disadvantages of Within-Subjects Design

Advantages:

• Smaller Sample Size: Within-subjects designs require fewer participants than between-subjects designs because the same participants are used for all treatments. This can be a significant advantage when the sample size is limited.
• Reduced Errors from Individual Differences: Within-subjects designs control for individual differences among participants by ensuring that all participants receive all treatments. This reduces the likelihood that individual differences will confound the results of the experiment.

Disadvantages:

• Carryover Effects: Carryover effects occur when the effects of one treatment carry over to the following treatment. This can bias the results of the experiment if the carryover effects are not controlled for.
• Participant Fatigue: Participant fatigue can occur when participants are required to participate in multiple treatments. This can lead to decreased motivation and attention, which can also bias the results of the experiment.
• Practice Effects: Practice effects occur when participants improve their performance on a task simply because they have practiced it multiple times. This can bias the results of the experiment if the practice effects are not controlled for.

Example of a Within-Subjects Design

• A researcher conducting an experiment on exercise and memory might have all participants try yoga before taking a memory test, then have all the participants try jogging before taking another memory test. The researcher could then compare the test scores to determine which type of exercise, yoga or jogging, had a more significant effect on performance on the memory tests.

Within-Subjects Design vs. Between-Subjects Design

• In a within-subjects design, all participants receive every treatment.
• In a between-subjects design, participants only receive one treatment.

Conclusion

Within-subjects designs can be a powerful tool for researchers, but they also have some potential drawbacks. Researchers should carefully consider the advantages and disadvantages of within-subjects designs before deciding whether to use one in their research.