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The basic idea behind this type of study is that participants can be part of the treatment group or the control group, but cannot be part of both. If more than one treatment is tested, a completely new group is required for each.
What is a Between Subjects Design?A group of researchers wants to test some modifications to the educational program and decide upon three different modifications. They pick a school and decide to use the four existing classes within an age group, assuming that the spread of abilities is similar. Each group of children is given a different educational program, along with a control group sticking with the original. All of the groups are tested, at the end, to determine which program delivered the most improvement. If the researchers want to be a little more accurate and reduce the chances of differences between the groups having an effect, they use modifications of the design. For example, maybe one class had a great teacher and has always been much more motivated than the others, a factor that would undermine the validity of the experiment. To avoid this, randomization and matched pairs are often used to smooth out the differences between the groups. Advantages of Between Subjects DesignBetween subjects designs are invaluable in certain situations, and give researchers the opportunity to conduct an experiment with very little contamination by extraneous factors. This type of design is often called an independent measures design because every participant is only subjected to a single treatment. This lowers the chances of participants suffering boredom after a long series of tests or, alternatively, becoming more accomplished through practice and experience, skewing the results. Disadvantages of Between Subjects DesignThe main disadvantage with between subjects designs is that they can be complex and often require a large number of participants to generate any useful and analyzable data. Because each participant is only measured once, researchers need to add a new group for every treatment and manipulation.
These factors could very easily become confounding variables and weaken the results, so researchers have to be extremely careful to eliminate as many of these as possible during the research design. These disadvantages are certainly not fatal, but ensure that any researcher planning to use a between subjects design must be very thorough in their experimental design. What is one difference between a within subjects design and a matched subjects design?A within subjects design tests the same people whereas a matched subjects design comes as close as possible to that and even uses the same statistical methods to analyze the results. This eliminates the possibility of differences between individuals affecting the results.
What is the difference between within subjects and between subjects research designs?Between-subjects (or between-groups) study design: different people test each condition, so that each person is only exposed to a single user interface. Within-subjects (or repeated-measures) study design: the same person tests all the conditions (i.e., all the user interfaces).
What is an example of a within subjects design?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.
How many groups of participants would be needed to completely counterbalance a within subjects experiment with four treatment conditions?For even four treatment conditions, 24 groups would be needed for a completely counterbalanced design.
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