Friday, 3 October 2014


While Single Subject Experiment have been used to evaluate macro-level effects on neighborhoods, communities, and even larger systems, their typical units of analysis have been smaller systems such as families and individuals. 
These experiments are used more frequently for applied research (establishing the utility of specific interventions) than for basic research (establishing scientific principles). They are even more frequently used to provide feedback to workers and clients about the progress of an individual intervention program than they are used in formal evaluation research. 
Single Subject Experiments involve repeated, systematic measurement of a dependent variable before, during, and after the manipulation of an independent variable. Usually, the dependent variable is some characteristic of an individual human being and the independent variable involves the application of some intervention. 
Traditionally, there have been two ways of evaluating intervention outcomes - individual case studies and group studies. Both these techniques have provided valuable information, but both have their drawbacks. Before investigating Single Subject Experiment further, let us see the explanation from this paper.

A.    Definition of Single Subject Experiment

Single Subject Experiment is Experiment using single participants in common. Has been done since the beginnings of psychology. Early researchers used prior to 1930. Solution to the problem of reliability and validity-extensive observations and frequent replication of results. Traditional premise was individual participants are essentially equivalent. Therefore, one should study additional participants only to make sure the original was not extremely abnormal.

Single-subject experimental designs represent an important tool in the development and implementation of evidence-based practice in communication sciences and disorders.

B.     Control Strategies in Single Subject Experiment

1.    Baseline

The measure of behavior before treatment that establishes a reference point for evaluating the effect of treatment. Servers two purposes: Descriptive and Predictive.

2.    Descriptive

Behavior that occurs before manipulation is measured to establish the baseline upon which to measure the later behavior.

3.    Predictive

Predicts what the behavior would be in the future in no treatment were administered.

4.    Trend

Variability from baseline that is systematic. Indicates a distinctive direction of the DV. Can be ascending or descending.

5.    Intervention

Repeated measure of behavior (Dependent Variable) under treatment (Independent Variable). Should cause a change from baseline. Clinical Significance: Effects must be large enough to reach. The practical importance of a result. Group experiments that find small but significant effects may have little clinical significance.

C.    Components of Single Subject Experiment
1.      Specify the problem
·         Identify the behavior that needs to be changed or treated
·         The behavior must be specified as clearly as possible in order for it to be reliably measured
2.      Select the design
·         There are a variety of  designs that are defined by different phases:
v Select design on basis of question want to answer
v Withdrawal, reversal or  designs answer question “is treatment effective?”
v Interaction designs answer question, “what are the interactive components of treatment?”
v And answer question, “which treatment is more effective?”
·         Phases in the designs consist basically of a baseline and the phases.
·         These phases can be combined in different ways to derive different designs
3.      Measure the problem
After the behavior has been clearly defined, the clinician decides how the behavior will be measured, e.g., correct/incorrect responses, rate of response, length of response, etc.
4.      Repeated measures
5.      The behavior is repeatedly measured before, during, and after treatment to determine if any changes have occurred in that behavior.
a.       This component is the hallmark of single-subject designs
6.      Baseline
·         Before treatment is initiated, the behavior is measured over a period of time (1-2 weeks, few days)
·         The baseline provides a comparison of “before” and “after” treatment in order to evaluate the effectiveness of the treatment approach
7.      Analysis of data
Single-subject designs rely on visual analysis of the graphed data rather than on statistical analysis of the data to make decisions about the significance of the treatment approach: slope, trend, and level of graphed data.

D.    Advantages and Disadvantages of Single Subject Experiment

1.    Advantages

a.       Practical and Ethical

problems can be addressed, Flexibility in Design, and Power

b.      Practical and Ethical

When research involves testing the effectiveness of a treatment that will benefit a participant, an ethical question arises. Ethics of placing some participants in a control group where they will not receive possibly beneficial treatment. Particularly important when working with a suicide prone population. Solution is to treat all participants but evaluate from a single subject standpoint.

c.       Flexibility in Design

An experiment on a group of subjects must be designed so all subjects receive the same experience and can be compared. Can be problems with designing experiments so they are best for all subjects. If a single subject design, can be modified on the spot by altering instructions or switching reinforcers.

2.    Disadvantages of Single Subject

a.       Alternating Treatment Design

Type of single participant design that allows the comparison of two different independent variables. Important to vary only one thing at a time in single participant research. If two variables change simultaneously, it's impossible to decide whether change in behavior is caused by one or the other or by the two together. Occasionally important to evaluate the effects of two or more different treatments to assess which would be most effective.

E.     Characteristic of Single Subject Experiment
James H. McMillan has summarized five characteristics of single-subject research.
1.    Reliable measurement: Since these designs involve multiple measures of behavior, it is important for the instrumentation to be reliable. Conditions for data collection, such as time of day and location, should be standardized, and observers need to be trained. Consistency in measurement is especially crucial in the transition before and after the treatment.
2.    Repeated measurement: The same behavior is measured over and over again. This step is different from most experiments, in which the dependent variable is measured only once. Repeated measures are needed to obtain a clear pattern or consistency in the behavior over time. They control for the normal variation of behavior that is expected within short time intervals. This aspect of single-subject designs is similar to time series studies, which investigate groups rather than individuals and do not provide for a return to conditions that were present before the treatment was implemented.
3.    Description of conditions: A clear, detailed description of the conditions of measurement and the nature of the treatment is needed to strengthen internal and external validity.
4.    Baseline and treatment conditions: Each single-subject study involves at least one baseline and one treatment condition. The baseline refers to a period of time in which the target behavior (dependent variable) is observed and recorded as it occurs without a special or new intervention. The baseline behavior provides the frame of reference against which future behavior is compared. The term baseline can also refer to a period of time following a treatment in which conditions match what was present in the original baseline. The treatment condition is a period of time during which the experimental manipulation is introduced and the target behavior continues to be observed and recorded. Both the baseline and treatment phases of the study need to be long enough to achieve stability in the target behavior.
5.    Single-variable rule: During a single-subject study, only one variable should be changed from baseline to treatment conditions. In some studies two variables are changed together during the same treatment condition. This is an interaction in single-subject research.

F.     Types of Single Subject Experiment
There are three commonly accepted types of single subject research designs.
1.      A-B-A Withdrawal Designs
In the A-B-A withdrawal family of single subject design strategies, A refers to the non-treatment or control phase of the experiment while B refers to the treatment phase of the experiment.
The simplest variant of A-B-A withdrawal designs is the A-B design. In this design type a non-treatment phase is initiated until the behavior in question demonstrates stability. Once the behavior becomes stable, the treatment phase is initiated.
2.      Multiple-Baseline Designs
In the typical single-subject designs we have considered a single subject, one behavior, and a single setting. In a multiple-baseline design, we systematically vary one of the three parameters (subject, behavior, or setting) while keeping the other two parameters constant. In the designs we have considered so far we have kept all three parameters constant. That is we have considered a single behavior for a single subject in a single setting. What if we looked at the number of words read correctly in one minute by three subjects while using their favorite color of transparency. In this design, we do a baseline line condition (that is reading words without using a colored filter) for all three subjects. After 3-5 trials, one of the subjects is subjected to the experimental condition (using a colored overlay) while the other two subjects continue with the baseline condition. After 3-5 more trials, the first subject is returned to the baseline condition while a second student goes into the experimental phase. The third student continues with the baseline condition. After 3-5 more days, the third student starts the experimental phase, while the other two students, return to or continue in the baseline or control situation.
3.      Alternating treatments Design
The final type of single research designs we will consider is the alternating treatments design. In this design we wish to compare the effect of two treatments on a subject. The subject in an alternating treatments design is given one of two treatments at each experimental session. Which treatment to use during a given session is determined randomly. This could be done by flipping a coin after assigning treatment 1 to heads and treatment 2 to tails. We could use this design with our colored transparencies in reading by considering the use of a clear transparency as treatment 1 and the use of a preferred colored transparency as treatment


Single Subject design is used to demonstrate a functional relationship between changes in the IV and the resultant changes in the DV. it provides an empirical verification that behavior change occurred because intervention occurred and no other cause. Single subject research (also known as single case experiments) is popular in the fields of special education and counseling. This research design is useful when the researcher is attempting to change the behavior of an individual or a small group of individuals and wishes to document that change. Unlike true experiments where the researcher randomly assigns participants to a control and treatment group, in single subject research the participant serves as both the control and treatment group. The researcher uses line graphs to show the effects of a particular intervention or treatment.  An important factor of single subject research is that only one variable is changed at a time. Single subject research designs are "weak when it comes to external validity....Studies involving single-subject designs that show a particular treatment to be effective in changing behavior must rely on replication, across individuals rather than groups--if such results are be found worthy of generalization”.
Single subject research design is a type of research methodology characterized by repeated assessment of a particular phenomenon (often a behavior) over time and is generally used to evaluate interventions. Repeated measurement across time differentiates single subject research design from case studies and group designs, as it facilitates the examination of client change in response to an intervention. Although the use of single subject research design has generally been limited to research, it is also appropriate and useful in applied practice.



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