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Chapter 11

Chapter 11 - Detailed


Department
Psychology
Course Code
PSYB01H3
Professor
Connie Boudens
Chapter
11

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Chapter 11 – Single Case, Quasi-Experimental and Developmental Research
SINGLE CASE EXPERIMENTAL DESIGNS
Single case experimental designs have traditionally been called single-subject designs, but now
the terms used are single case and single participant
Single case experiments were developed from a need to determine whether an experimental
manipulation had an affect on a single research participant. In a single case deign, the subjects
behavior is measured over time during a baseline control period. The manipulation is then
introduced during a treatment period, and the subjects behavior continues to be observed
Baseline: in a single case study design, the subjects behavior during a control period before
introduction of the experimental manipulation
A change in the subjects behavior from baseline to treatment periods is evidence for the
effectiveness of the manipulation. The problem, however, is that there could be many explanations
for the change other than the experimental treatment (called alternative explanations)
Reversal Designs
oThe basic issue in single case experiments is how determine that the manipulation of the
independent variable has an affect
oOne method is to demonstrate the reversibility of the manipulation
oA simple reversal design takes the following form:
A (baseline period) B (treatment period) A (baseline period)
oThis design, called ABA design requires that behavior be observed during the baseline
control (a) period and again during the treatment (b) period, and also during a second
baseline (a) period after the experimental treatment has been removed (sometimes called
a withdrawal design, in recognition of that fact that the treatment is removed or
withdrawn)
oThe ABA design can be greatly improved by testing the treatment multiple times (ABAB
or ABABAB) to address 2 problems with the ABA reversal design: first, a single reversal
is not extremely powerful evidence for the effectiveness of the treatment and the single
problem is ethical; it doesnt seem right to end the design with the withdrawal of a
treatment that may be very beneficial for the participant
oA control group may also be used in a reversal design
Multiple Baseline Designs
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oMultiple measures over time can be made before and after the manipulation
oIf the manipulation is effective, a change in behavior will be immediately observed, and
the change will continue to be reflected in further measures of the behavior
oIn a multiple baseline design, the effectiveness of the treatment is demonstrated when a
behavior changes only after the manipulation is introduced—to demonstrate the
effectiveness of the treatment, such a change must be observed under multiple
circumstances to rule out the possibility that other events were responsible
oSeveral variations:
In multiple baseline across subjects, the behavior of several subjects is measured
over time; for each subject, though, the manipulation is introduced at a different
point in time
In multiple baseline across behaviors, several different behaviors of a single-
subject are measured over time. At different times, the same manipulation is
applied to each of the behaviors
The third variation is multiple baseline across situations, in which the same
behavior is measured in different settings, such as at home and at work.
Replications in Single Case Designs
oThe procedures for use with a single subject can, of course, be replicated with other
subjects, greatly enhancing the generalizability of the results
oThe tradition of single case research has been to present the results from each subject
individually rather than a group
Grouping data can be misleading
PROGRAM EVALUATION
Program evaluation is research on programs that are proposed and implemented to achieve some
positive effect on a group of individuals
Rossi et al. identify five types of evaluations; each attempts to answer a different question about
the program
oNeed: Needs assessment studies ask whether they are, in fact, problems that need to be
addressed in a target population—once a need has been established, programs can be
planned to address the need
oProgram theory: Assessment of program theory as the program must be based on valid
assumptions about the causes of the problems and the rationale of the proposed program
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