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CHAPTER 9
SINGLE-CASE RESEARCH DESIGNS
CHAPTER OUTLINE AND OBJECTIVES
I. Overview
II. The Case Study Method
A. Characteristics
Case studies, intensive descriptions and analyses of individuals, lack the degree of control found
in small-n experimental designs.
Case studies are a source of hypotheses and ideas about normal and abnormal behavior.
B. Advantages of the Case Study Method
Case studies provide new ideas and hypotheses, opportunities to develop new clinical
techniques, and a chance to study rare phenomena.
Scientific theories can be challenged when the behavior of a single case contradicts theoretical
principles or claims, and theories can receive tentative support using evidence from case studies.
Idiographic research (the study of individuals to identify what is unique) complements nomothetic
research (the study of groups to identify what is typical).
C. Disadvantages of the Case Study Method
Researchers are unable to make valid causal inferences using the case study method because
extraneous variables are not controlled and several “treatments” may be applied simultaneously
in case studies.
Observer bias and biases in data collection can lead to incorrect interpretations of case study
outcomes.
Whether results from a case study may be generalized depends on the variability within the
population from which the case was selected; some characteristics (e.g., personality) vary more
across individuals than others (e.g., visual acuity).
D. Thinking Critically about Testimonials Based on a Case Study
Being mindful of the limitations of the case study method can be helpful when evaluating
individuals’ testimonials about the effectiveness of a particular treatment.
III. Single-Case (Small-n) Experimental Designs
In applied behavioral analysis, the methods developed within the experimental analysis of behavior
are applied to socially relevant problems.
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A. Characteristics of Single-Case Experiments
Researchers manipulate an independent variable in single-case experiments; therefore, these
designs allow more rigorous control than case studies.
In single-case experiments, baseline observations are first recorded to describe what an
individual’s behavior is like (and predicted to be like in the future) without treatment.
Baseline behavior and behavior following the intervention (treatment) are compared using visual
inspection of recorded observations.
B. Specific Experimental Designs
In the ABAB design, baseline (A) and treatment (B) stages are alternated to determine the effect
of treatment on behavior.
Researchers conclude that treatment causes behavior change when behavior changes
systematically with the introduction and withdrawal of treatment.
Interpreting the causal effect of the treatment is difficult in the ABAB design if behavior does not
reverse to baseline levels when treatment is withdrawn.
Ethical considerations may prevent psychologists from using the ABAB design.
In multiple-baseline designs, a treatment effect is shown when behaviors in more than one
baseline change only following the introduction of a treatment.
Multiple baselines may be observed across individuals, behaviors, or situations.
Interpreting the causal effect of treatment is difficult in multiple-baseline designs when changes
are seen in a baseline before an experimental intervention; this can occur when treatment effects
generalize.
C. Problems and Limitations Common to all Single-Case Designs
Interpreting the effect of a treatment can be difficult if the baseline stage shows excessive
variability or increasing or decreasing trends in behavior.
The problem of low external validity with single-case experiments can be reduced by testing small
groups of individuals.
IV. Summary
REVIEW QUESTIONS AND ANSWERS
These review questions appear in the textbook (without answers) at the end of Chapter 9, and can be
used for a homework assignment or exam preparation. Answers to these questions appear in italic.
1. Identify and give an example of each of the advantages of the case study method.
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2. Distinguish between a nomothetic and an idiographic approach to research.
3. Identify and give an example of each of the disadvantages of the case study method.
4. What is the major limitation of the case study method in drawing cause–effect conclusions?
5. Under what conditions might a single-case design be more appropriate than a multiple-group design?
6. Distinguish between baseline and intervention stages of a single-case experimental design.
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7. Why is an ABAB design also called a reversal design?
8. What methodological problems are specifically associated with an ABAB design?
9. Outline the general procedures and logic that are common to all the major forms of multiple-baseline
designs.
10. What methodological problems are specifically associated with multiple-baseline designs?
11. What methodological problems must be addressed in all single-case designs?
12. What evidence supports the external validity of single-case designs?
individuals is used in a single-case experimental design. (p. 299)
CHALLENGE QUESTIONS AND ANSWERS
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These questions appear in the textbook at the end of Chapter 9, and can be used for a homework
assignment, in-class discussion, or exam preparation. Answers to these questions appear in italic below.
[Answer to Challenge Question 1 also appears in the text.]
1. A case study showing how “mud therapy” was successful in treating an individual exhibiting excessive
anxiety was reported in a popular magazine. The patient’s symptoms included trouble sleeping, loss
of appetite, extreme nervousness when in groups of people, and general feelings of arousal that led
the individual always to feel “on edge” and fearful. The California therapist who administered the mud
therapy was known for this treatment, having appeared on several TV talk shows. He first taught the
patient a deep relaxation technique and a “secret word” to repeat over and over in order to block out
all disturbing thoughts. Then the patient was asked to lie submerged for 2 hours each day in a special
wooden “calm tub” filled with mud. During this time the patient was to practice the relaxation
exercises and to concentrate on repeating the secret word whenever the least bit of anxiety was
experienced. The therapy was very costly, but after 6 weeks the patient reported to the therapist that
he no longer had the same feelings of anxiety that he reported previously. The therapist pronounced
him cured and attributed the success of the treatment to immersion in the calming mud. The
conclusion drawn by the author of the magazine article describing this therapy was that “it is a
treatment that many people could benefit from.” On the basis of your knowledge of the limitations of
the case study method, answer the following questions:
A. What possible sources of bias were there in the study?
B. What alternative explanations can you suggest for the successful treatment?
C. What potential problem arises from studying only one individual?
2. A 5-year-old child frequently gets skin rashes, and the mother has been told by her family doctor that
the problem is due to “something” the child eats. The doctor suggests that she “watch carefully” what
the child eats. The mother decides to approach this problem by recording each day whether the child
has a rash and what the child ate the day before. She hopes to find some relationship between eating
a particular food and the presence or absence of the rash. Although this approach might help
discover a relationship between eating certain foods and the appearance of the rash, a better
approach might be one based on the logic and procedures associated with single-case designs.
Explain how the mother might use such an alternative approach. Be specific and point to possible
problems that may arise in this application of behavioral methodology.
4. A teacher asks your help in planning a behavioral intervention that will help manage the behavior of a
problem child in his classroom. The child does not stay at her desk when asked to do so, does not
remain quiet during “quiet times,” and exhibits other behaviors that disrupt the teaching environment.
Explain specifically how a positive reinforcer, such as candy or small toys, might be used as part of a
multiple-baseline across behaviors design to improve the child’s behavior.
ISSUES AND PROBLEMS FOR CLASS DISCUSSION
1. Reading Research Critically
This research summary and the accompanying questions could be used in class for small group
discussion or as a test question. The answers appear below. The research summary and questions
appear on subsequent pages to facilitate photocopying.
Answers to Reading Research Critically: Kleptomania
A. Glover (1985) presented a case study describing the treatment of a woman with kleptomania
using covert sensitization. What evidence provided in the summary indicates that the treatment
caused the woman’s improvement? What evidence is lacking that would convince you that the
cause of the woman’s improvement was covert sensitization? Explain how a single-case
experiment might provide this evidence.
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Reading Research Critically
Read the following description of a research study to answer the questions that follow. [Based on an
article by: Glover, J. H. (1985). A case of kleptomania treated by covert sensitization. British Journal of
Clinical Psychology, 24, 213-214.
Kleptomania
Kleptomania is an uncontrollable urge to steal things without any motive for profit or gain. In this case
study, a therapist describes the successful treatment of a 56-year-old married woman who had been
“shoplifting every day for the previous 14 years.” She generally would shoplift on her lunch hour, obtaining
objects with no apparent purpose. For example, she might steal a pair of baby shoes but there would be
no baby to whom she might give the shoes. The woman told the therapist that on awakening each day
“she would have a compulsive thought that she must shoplift later that day.” She expressed “repugnance”
at the thought but found that she invariably would give in to it.
This individual’s compulsion to shoplift apparently began about a year after her husband had been
convicted of embezzlement and heavily fined. She was very upset by that experience and still found it
hard to forgive him. Because her husband could find only poor paying jobs she was forced to work full–
time, which she resented. She lost many of her friends following the husband’s criminal conviction and
over the years she had been on antidepressant medication. Only a few weeks prior to seeing the
therapist she had told her husband for the first time about the shoplifting. She also had confided in her
general practitioner at this time. She told the therapist that she finally could no longer deal with the
problem alone.
The woman agreed to be treated by covert sensitization. This process involved pairing imagery of nausea
and vomiting with the act of stealing. She was treated during a total of four sessions, one session every
two weeks. In the first three sessions, the therapist asked her to imagine “increasing nausea as she
approached an article” she was attempting to steal, to imagine vomiting in front of other shoppers as she
took the article, then to reduce the degree of imagined nausea as she returned the article and left the
store. In the final session, she was asked to imagine increasing nausea as she approached an object but
then to imagine the nausea “dissipating” as she turned away without taking the object. Hypnosis was also
used in the last two sessions. Between sessions she was asked to rehearse thinking about nausea and
vomiting several times daily, and to leave at home a particular bag she had used when shoplifting.
During the 8-week period of therapy her compulsion to shoplift diminished. She stole only four objects
during the treatment period. Nineteen months after the completion of covert sensitization therapy, she
had lapsed and shoplifted only one time. She reported feeling better about herself and had begun to seek
out social contacts. The thought of shoplifting when it did occur was usually accompanied by an “unwell”
feeling that she could remove “by walking away from any tempting article.”
A. Glover (1985) presented a case study describing the treatment of a woman with kleptomania using
covert sensitization. What evidence provided in the summary indicates that the treatment caused the
woman’s improvement? What evidence is lacking that would convince you that the cause of the
woman’s improvement was covert sensitization? Explain how a single-case experiment might provide
this evidence.
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B. Is there any reason to believe that a single-case experiment would be unethical in treating
kleptomania? Explain.
2. More Challenges
This additional challenge question (along with the concepts illustrated in the question) can be used for
class discussion or as a possible test question.
You have been asked to give a lecture in an introductory psychology class on the topic of single-case
research designs. You decide to begin the lecture by contrasting the relative advantages and
disadvantages of the case study method and the single-case experimental design. Indicate what
points you would highlight in the outline for this part of your lecture.
3. Designing Single-Case Experiments
As a class or in small groups, students could be asked to design a multiple-baseline experiment
and/or an ABAB experiment to address a specific problematic behavior. If students work in small
groups, some groups could design an ABAB experiment and some groups could design a multiple-
baseline experiment (these groups could be differentiated further according to whether multiple–
baselines across individuals, behaviors, or situations are employed). The research designs could then
be compared during class discussion in order to discuss advantages and disadvantages associated
with each design. This comparison will be more instructive if each group attempts to address the
same problematic behavior.
If the problematic behavior is described in general terms an essential step in this task will be to
specify clearly the behavior, including antecedents and consequences of the behavior, and
procedures for measuring the behavior. Students might find it especially instructive if the problematic
behavior is one they or their friends or family experience (e.g., overeating, cigarette smoking,
procrastination).
4. Literature Search
It is our experience that few students have seen or are even aware of the Journal of Applied Behavior
Analysis (JABA), which publishes almost exclusively results of single-case studies. A useful exercise
is to ask students to look through issues of JABA and identify articles that interest them and which
use one of the single-case methodologies discussed in this chapter. If students print the Abstract of
the article and bring it to class then class discussion can revolve around types of studies where
single-case methodologies have been used. Students may be asked to look specifically for examples
in areas other than clinical psychology, for example, educational or business applications.
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It may be interesting to contrast students’ search of psychological literature with a search for
“testimonials” from the popular press. Students may be asked to discuss the scientific (or
nonscientific) merits of testimonials and identify the evidence needed to increase their acceptance of
findings in support of treatments.
LEARNING BY DOING RESEARCH
Although there may be few opportunities for students to actually carry out a single-case experiment in the
context of a research methods class, it certainly is possible (and perhaps desirable) to ask students to
design single-case studies to provide evidence for various treatments (see #3 in “Issues and Problems for
Class Discussion”). Many treatments of interest to researchers outside the realm of clinical psychology
have been assessed using methodologies associated with single-case designs, although frequently
applied to groups of individuals. For example, single-case methodology has been extended to study
interventions aimed at increasing the use of designated drivers to reduce alcohol-related driving accidents
[Brigham, T. A., Meier, S. M., & Goodner, V. (1995). Increasing designated driving with a program of
prompts and incentives. Journal of Applied Behavior Analysis, 28, 83-84.] Researchers used an ABAB
design in which the treatment involved placing posters and table signs offering free nonalcoholic drinks to
designated drivers at bars frequented by college students.
Students can be asked to work in small groups to describe how they might use an extension of single–
case methodologies to “groups” in order to provide evidence for the effect of the following interventions:
• energy conservation program on campus
• promotional signs in fast-food restaurant or other eatery
• an anti-littering campaign
• community recycling program
Students should be encouraged to consider both ABAB designs and multiple-baseline designs in their
research proposals, and to be very specific about how behaviors will be measured and recorded, length
of baseline and treatment phases, etc. This exercise has the added advantage of revealing to students
how research methods can be valuable to individuals involved with program evaluation of “real world”
interventions.
INSTRUCTOR’S LECTURE/DISCUSSION AIDS
The following pages reproduce content from Chapter 9 and may be used to facilitate lecture or
discussion.
1. Single-Case Research Designs: This page introduces single-case research and provides an overview
of the case study method.
2. Case Study Method vs. Single-Case Experiments: This page describes testimonials as non-scientific
and introduces single-case experiments.
3. Baseline Stage: The importance of a baseline stage is described on this page.
5. ABAB Design: This page illustrates a treatment effect in an ABAB design and a situation in which a
reversal does not occur.