Finally, the researcher removes the treatment and again waits until the dependent variable reaches a steady state. Again, the researcher waits until that dependent variable reaches a steady state so that it is clear whether and how much it has changed. There may be a period of adjustment to the treatment during which the behaviour of interest becomes more variable and begins to increase or decrease. When steady state responding is reached, phase B begins as the researcher introduces the treatment. This is the level of responding before any treatment is introduced, and therefore the baseline phase is a kind of control condition. During the first phase, A, a baseline is established for the dependent variable. The most basic single-subject research design is the reversal design, also called the ABA design. The effect of an independent variable is easier to detect when the “noise” in the data is minimized. Recall that we encountered this same principle when discussing experimental research more generally. The idea is that when the dependent variable has reached a steady state, then any change across conditions will be relatively easy to detect. This is sometimes referred to as the steady state strategy (Sidman, 1960). Specifically, the researcher waits until the participant’s behaviour in one condition becomes fairly consistent from observation to observation before changing conditions. Instead, it depends on the participant’s behaviour. (This is called a reversal design and will be discussed in more detail shortly.) Figure 10.2 Results of a Generic Single-Subject Study Illustrating Several Principles of Single-Subject ResearchĪnother important aspect of single-subject research is that the change from one condition to the next does not usually occur after a fixed amount of time or number of observations. Thus Figure 10.2 represents a design in which the participant was tested first in one condition (A), then tested in another condition (B), and finally retested in the original condition (A). The conditions are often designated by capital letters: A, B, C, and so on. Second, the study is divided into distinct phases, and the participant is tested under one condition per phase. First, the dependent variable (represented on the y-axis of the graph) is measured repeatedly over time (represented by the x-axis) at regular intervals. Many of these features are illustrated in Figure 10.2, which shows the results of a generic single-subject study. General Features of Single-Subject Designsīefore looking at any specific single-subject research designs, it will be helpful to consider some features that are common to most of them. Interpret the results of simple single-subject studies based on the visual inspection of graphed data.Explain how single-subject research designs address the issue of internal validity. Design simple single-subject studies using reversal and multiple-baseline designs.Describe the basic elements of a single-subject research design.
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