Question

A. The most commonly used single-subject designs are the ABAB design and the multiple-baseline design. Describe the various circumstances for which each of these designs is appropriate.

Answer 1

There are certain experimental conditions in which single subject design is useful. These conditions are-

1. It provides an efficient tool for evidence based practice where more than one subject is not required.
2. If the effectiveness of an experimental treatment is to be judged then single subject design is the best way. But care must be exercised in ensuring that extraneous variables are properly controlled and error variance is minimum.
3. There is no need for a control group.
4. Single-subject designs are most commonly used to study the changes in behavior an individual exhibits after exposure to a treatment or intervention of some sort.
5. The basic approach of researchers using an A-B design is to expose the same subject, operating as his or her own control, to two conditions or phases.

This indicates that single subjects designs are best suited in the above circumstances. There are many single subjects designs- ABAB and Multiple Baseline designs.

The most basic single-subject research design is the reversal design, also called the ABA design. During the first phase, A, a baseline is established for the dependent variable. This is the level of responding before any treatment is introduced, and therefore the baseline phase is a kind of control condition. When steady state responding is reached, phase B begins as the researcher introduces the treatment. There may be a period of adjustment to the treatment during which the behavior of interest becomes more variable and begins to increase or decrease. Again, the researcher waits until that dependent variable reaches a steady state so that it is clear whether and how much it has changed. Finally, the researcher removes the treatment and again waits until the dependent variable reaches a steady state. This basic reversal design can also be extended with the reintroduction of the treatment (ABAB), another return to baseline (ABABA), and so on.

There are two potential problems with the reversal design—both of which have to do with the removal of the treatment. One is that if a treatment is working, it may be unethical to remove it. For example, if a treatment seemed to reduce the incidence of self-injury in a developmentally disabled child, it would be unethical to remove that treatment just to show that the incidence of self-injury increases. The second problem is that the dependent variable may not return to baseline when the treatment is removed. For example, when positive attention for studying is removed, a student might continue to study at an increased rate. This could mean that the positive attention had a lasting effect on the student’s studying, which of course would be good. But it could also mean that the positive attention was not really the cause of the increased studying in the first place. Perhaps something else happened at about the same time as the treatment—for example, the student’s parents might have started rewarding him for good grades.

Therefore, it may be concluded that single subjects design are very much in use.