Awithin-subject design is a type of experimental design in which all participants are exposed to every treatment or condition. It is also known as a repeated measures design. Show
The term "treatment" is used to describe the different levels of the independent variable, the variable that's controlled by the experimenter. In other words, all of the subjects in the study are treated with the critical variable in question. This article discusses what a within-subjects design is, how this type of experimental design works, and how it compares to a between-subjects design. Within-Subjects Design vs. Between SubjectsLet's imagine that you are doing an experiment on exercise and memory. For your independent variable, you decide to try two different types of exercise: yoga and jogging. Instead of breaking participants up into two groups, you have all the participants try yoga before taking a memory test. Then, you have all the participants try jogging before taking a memory test. Next, you compare the test scores to determine which type of exercise had the greatest effect on performance on the memory tests. This within-subjects design can be compared to what is known as a between-subjects design. In a between-subjects design, people are only assigned to a single treatment. So one group of participants would receive one treatment, while another group would receive a different treatment. The differences between the two groups would then be compared. Consider the earlier example of the experiment looking at exercise and memory. In a between-subjects design, one group of participants would do yoga and then take a memory test. A different group of participants would jog and then take the memory test. Afterward, the results of the memory tests would be compared to see how the type of exercise influenced memory. RecapIn a within-subjects design, all participants receive every treatment. In a between-subjects design, participants only receive one treatment. Advantages of Within-Subjects DesignWhy exactly would researchers want to use a within-subject design? One of the most significant benefits of this type of experimental design is that it does not require a large pool of participants. A similar experiment in a between-subject design, which is when two or more groups of participants are tested with different factors, would require twice as many participants as a within-subject design. A within-subject design can also help reduce errors associated with individual differences. In a between-subject design where individuals are randomly assigned to the independent variable or treatment, there is still a possibility that there may be fundamental differences between the groups that could impact the experiment's results. In a within-subject design, individuals are exposed to all levels of a treatment, so individual differences will not distort the results. Each participant serves as their own baseline. Disadvantages of Within-Subjects DesignThis type of experimental design can be advantageous in some cases, but there are some potential drawbacks to consider. A major drawback of using a within-subject design is that the sheer act of having participants take part in one condition can impact the performance or behavior on all other conditions, a problem known as a carryover effect. So for instance in our earlier example, having participants take part in yoga might have an impact on their later performance in jogging and may even affect their performance on later memory tests. Fatigue is another potential drawback of using a within-subject design. Participants may become exhausted, bored, or less motivated after taking part in multiple treatments or tests. Finally, performance on subsequent tests can also be affected by practice effects. Taking part in different levels of the treatment or taking the measurement tests several times might help the participants become more skilled. This means they may be able to figure out how to game the results in order to do better on the experiment. This can skew the results and make it difficult to determine if any effect is due to the different levels of the treatment or simply a result of practice. Frequently Asked Questions
By Kendra Cherry
Thanks for your feedback! What are conditions in an experiment that are the same for all groups?Constant - The factors that do not change during the experiment. Control - The control is the group that serves as a standard of comparison. It is exposed to the same conditions as the experimental group, except for the variable being tested.
What is a matched group design?A matched group design is an experimental design where the participants in the study are chosen because they have variables that match each other. The variables can be anything that might affect the results of the study, for example, height, weight, age, etc.
What is simultaneous withinSimultaneous Within-Subjects Designs
Instead of having people make judgments about all 10 defendants of one type followed by all 10 defendants of the other type, the researcher could present all 20 defendants in a sequence that mixed the two types.
What is group equivalence in research?In the simplest type of experiment, we create two groups that are “equivalent” to each other. One group (the program or treatment group) gets the program and the other group (the comparison or control group) does not. In all other respects, the groups are treated the same.
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