Single- Subject Research Designs
Chapter 14 Single- subject designs
Single- subject designs, or single- case designs, are research designs that use the results from a single participant or subject to establish the existence of cause- and- effect relationships. Evaluating the Results from a Single- Subject Study
a single- subject design does not provide researchers with a set of scores from a group of subjects Instead, the presentation and interpretation of results from a single- subject experiment are based on visual inspection of a simple graph of the data. Example Limitation The results as presented do not represent a true experiment because there is no control over extraneous variables. Phases and phase changes
A phase is a series of observations of the same individual under the same conditions. When no treatment is being administered, the observations are called baseline observations. 3 types of baseline Stable level Stable trend Unstable data Dealing With Unstable Data
The researcher can simply wait; occasionally, a participant reacts unpredictably to the novelty of being observed. Dealing With Unstable Data
2. Consider the average of a set of two ( or more) observations. Dealing With Unstable Data
3. look for patterns within the inconsistency. For example, a researcher examining disruptive classroom behavior may find that a student exhibits very high levels of disruption on some days and very low levels on other days. days she has a swimming lesson Length of a Phase To establish a pattern ( level or trend) within a phase and to determine the stability of the data within a phase, a phase must consist of a minimum of three observations. When to Change Phases When the data in a baseline phase show a trend indicating improvement in the clients behavior, a researcher should not intervene by introducing a treatment phase. Another possibility is that the baseline data indicate a seriously high level of dangerous or threatening behavior. In this case, a researcher probably should not wait for the full set of five or six observations necessary to establish a clear pattern. When to stop treatment If a treatment appears to produce an immediate and severe deterioration in behavior, we should stop the treatment Visual Inspection Techniques
Unfortunately, there are no absolute, objective standards for determining how much of a change in pattern is sufficient to provide a convincing demonstration of a treatment effect. The most convincing results occur when the change in pattern is immediate and large. 4 types of change Change in average level Immediate change in level
Change in trend Latency of change. 1- Change in average level 2- Immediate change in level
Comparing the last point in one phase with the first point in the following phase 2- immediate change in level 3- Change in trend 4- Latency in change 4- Latency in change The problem with single subject design THE ABAB REVERSAL DESIGN
the majority of single- subject research studies use ABAB design; consists of four phases: a baseline phase ( A), followed by treatment ( B), then a return to baseline ( A), and finally a repetition of the treatment phase ( B). Effective Not Effective Limitations of the ABAB Design
The clinician has implemented a treatment that has corrected a problem behavior, and when the treatment is removed, the correction continues. A second problem with an ABAB design concerns the ethical question of withdrawing a successful treatment. Variations on the ABAB Design 1- B not working use C 2- B not working add C B= Graduated exposure C= Reinforcement 3- MULTIPLE- BASELINE DESIGNS
1- Eliminates the need for a return to baseline and therefore, 2- Is particularly well suited for evaluating treatments with long- lasting or permanent effects. 3- MULTIPLE- BASELINE DESIGNS
Examples A therapist uses the same method for 2 differentbehaviors (across behaviors) For one behavior that is exhibited in 2 different situations. (across situations) A teacher uses the same method on 2 different students (across subjects) Person1 Person2 2 different students Yelling Crying 2 different behaviors School Home 2 different situations. Weaknesses of the Multiple- Baseline Design? Weaknesses of the Multiple- Baseline Design
The risk is that a treatment applied to one behavior may generalize and produce changes in the second behavior. (Treating stuttering may help treating aggressive behavior) In a multiple- baseline study across behaviors, one behavior may show a large and immediate change, but the second behavior may show only a minor or gradual change when the treatment is introduced. The same problem can occur with research involving different participants with similar behavior problems. 4- Dismantling design A dismantling design, also called a component- analysis design, consists of a series of phases in which each phase adds or subtracts one component of a complex treatment to determine how each component contributes to the overall treatment effectiveness. Example 5- The Changing- Criterion Design
The criterion level is changed from one phase to the next. Smoking Treatment 6-The Alternating- Treatments Design
In an alternating- treatments design, also called a discrete-trials design, two ( or more) treatment conditions are randomly alternated from one observation to the next. Example 1- Alternate weeks Example 2- 9 cases for each method GENERAL STRENGTHS OF SINGLE- SUBJECT DESIGNS
Is conducted with only one participant or occasionally a very small group. Tends to be much more flexible than a traditional group study. Single- subject designs require continuous assessment. General Weaknesses Of Single- Subject Designs
Participants behavior may be affected not only by the treatment conditions but also by the assessment procedures. Another concern for single- subject designs is the absence of statistical controls.