INTRODUCTION
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.
DISCUSSION
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
CONCLUSION
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.
REFERENCES
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