withholding of treatment by assigning certain partici-
pants to control groups or waiting lists. Some have
argued that studies that withhold treatment from
some clients, although representing good science,
are potentially unethical because they may deprive
people of hope for relief. Even though the therapy
to be used may be unproved—and even though
some assert that, in the interests of the ultimate good
of many people, science must deprive a few of the
possibility of improvement—the specter of ethics
still lurks in the background. Single-case designs, in
contrast, do include periods of treatment for all.
Another practical reason for using single-case
designs is that it is often extremely difficult in clinical
settings to find enough participants for matching or
random assignment to control groups. Single-case
studies reduce the numbers needed. Also, some
have argued that most research generalizes findings
based on mean scores. Consequently, the results may
not really apply to or characterize any one case.
Single-case designs sidestep such problems.
The ABAB Design. TheABAB design permits
measurement of a treatment’s effectiveness by sys-
tematic observation of changes in the participant’s
behavior as treatment and no-treatment conditions
alternate. It is called the ABAB design because the
initial baseline period (A) is followed by a treatment
period (B), a return to the baseline (A), and then a
second treatment period (B).
A good illustration of the ABAB single-case
approach is the study of Thomas, a 4-year-old
boy diagnosed with autism spectrum disorder
(Crozier & Tincani, 2007). The goal of this study
was to assess whether a particular intervention,
Social Stories, would help Thomas sit at the morn-
ing circle, attend to the teacher, and participate in
songs and stories each morning at his preschool.
Thomas was prone to roam around the classroom
and spend little time at the circle each morning. For
Thomas, the Social Story procedure involved a
researcher reading a tailored script to him while at
an empty table on the side of the room before circle
time. The script involved Thomas sitting at circle
time, attending to the teacher, and participating.
The target behavior that was coded was sitting
appropriately at the circle and not engaging in
activities that were not part of the circle time.
Figure 4-5 shows for each observation session
the percentage of time that Thomas exhibited the
desired target behavior. As can be seen, at the first
baseline before any intervention Thomas spent on
average only about 16% of the time sitting appro-
priately at the circle. Note that the sitting time for100806040200SessionsPercentage of Study Behavior5 10 15 20 25 30Baseline Reinforcement I Reversal Reinforcement IIF I G U R E 4-5 Thomas: Using Social Story intervention to improve sitting at circle time appropriately.
SOURCE: Crozier, S., & Tincani, M.,“Effects of Social Stories on prosocial behavior of preschool children with autism spectrum disorders,”
Journal of Autism and Developmental Disorders,37, (fig 1, p. 1809). Copyright © 2007 by Springer. Reprinted with permission.
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