Single-Case Research
Designs
PS1006 Lecture 6
Sam Cromie
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Group Vs Single Case Designs
Group designs:
• Average performance
of a group
• Comparing average
performance between
groups
• Group variability
• Statistical significance
Single case designs:
• Actual performance of
an individual
• Comparing individual
performance in
different conditions
• Individual variability
• Clinical significance
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Examples of SC Resesarch
• Ebbinghaus (1885) - participant and
experimenter - first systematic evidence of
forgetting over time
• Freud’s psychoanalytical case studies
• Behaviour Analysis – SC experiments with
pigeons, monkeys, humans
• Psychophysics, study of expert performance
e.g., chess players & musicians,
• Oliver Sacks - ‘The Man Who mistook His
Wife for a Hat’
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Single case studies - characteristics
• Intensive description and analysis of single
individual.
• Data obtained through: naturalistic
observation, interviews, psychological
tests, experimental measurement
• May describe the application and results of
a particular treatment.
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Case Studies (CS) vs Single Case
Experiments (SCE)
• Exploratory
• Qualitative
• May generate
hypotheses for
experimental
research
• Experimental
manipulation
• IVs and DVs
• Operational definition
• Measurement
• Hypotheses
• 6+ participants
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Advantages of Case studies
• Provide new ideas and hypotheses
– Open the way for discoveries based on
other methodologies
– Provides opportunity to develop new clinical
techniques
• Try out new clinical techniques the utility
of which may only become apparent in
specific cases
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Advantages
• Provides chance to study rare
phenomena
– Infrequent occurrences can only be
examined through intensive study e.g.,
• Feral children - ‘The wild boy of Aveyron’ Victor - Lived alone in woods from ages of 511/12
• ‘The forbidden experiment’ - Genie
– Such cases do not offer definitive answers
rather ‘obliges us to reflect on how to live
with these unsolved questions’ - (Shattuck,
1994, p182)
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Advantages
• Can support or challenge scientific theories
– Falsificationism
• Genie was found at 13 never having learned to
communicate due to lack of human interaction.
• Lenneberg proposed critical period of language
development = 2-puberty
• Lenneberg theory could be tested by determining
whether Genie could now acquire language.
• Genie showed some language development but was
never completely normal
• Lenneberg’s theory at the very least should be
modified after the evidence ‘provided’ by Genie
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Advantages
• Can support or challenge scientific
theories
– Atkinson and Shiffrin’s multi-storey theory of
memory gets considerable support from
patients who show specific breakdowns in
one part of the memory system.
– H.M. could have conversation and remember
events for short periods of time but could not
form new memories.
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Advantages
– Individual is more than can be represented
by the collection of average values on
various dimensions.
– Has the ability to reveal various nuances
and subtleties of behaviour that a group
approach may miss.
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Difficulties of Case studies
• Difficulty of drawing cause-effect
conclusions
– Illnesses can subside spontaneously
– Other aspects of the patient-therapist
relationship may have an impact
– Genie - a Doctor’s examination at 14mnths
lead to the comment that she was possibly
retarded - there is no way of concluding that
Genie’s disposition was a product of the poor
environment which she inhabited.
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Difficulties of Case studies
• Biases
– In interpretation
– Data collection. Archival records or information
based on self-reports are particularly vulnerable.
• Lack of generalisation
– Difficult to generalise from case to case.
– Except where it is assumed that the underlying
physiological/behavioural systems are shared
e.g. psychophysics assumes that for example
visual systems are based on a shared
physiological makeup
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Difficulties of Case studies
• Public often considers personal testimony
as measure of efficacy
– In 1980’s Laetrile, made from apricot pits,
supposed to be beneficial to the treatment of
cancer.
• By using Laetrile instead of traditional therapies,
many patients may have postponed valid courses
of treatment and thus contributed to the spread of
their cancer.
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Single-Case Experimental Designs
• Core tool of Behaviour Analysis (Skinner)
• Manipulating single IVs and measuring behavioural
change in one individual
• Baseline compared with intervention phases
• Assumes the behavioural principles are universal,
across individuals and organisms
• Graphical depiction of results
• Impact of results visually rather then statistically
determined – “if the difference is not obvious it is
not significant”
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Basic SC experimental designs
• A= Baseline; B= Intervention 1; C= Intervention 2
• AB – weak design
• ABA – reversal procedures adds to predictive power, but
ends up with baseline
• ABAB – even more predictive power and ends up with
intervention
• ABC, ABAC, ABCD, etc.
• Problems:
– ethics of withdrawal,
– intervention may have non-reversible effects – collateral
reinforcement, verbal behaviour
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AB design
Jack
A
25
B
Token Economy/ DRO.
Baseline
Inappropriate Vocalizations/Hitting
20
15
Series1
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
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25
No. of Days
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ABAB Design Experiment
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An ABC design experiment
Junior Infants
120
Baseline
Training
Token Economy
Off Task Percent
100
80
60
Series1
40
20
0
1
4
7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58
No of Sessions
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Multiple baseline designs
• An independent variable is sequentially applied
to at least two dependent variables
• Multiple baseline
– Across behaviours
– Across settings
– Across participants
• Avoid problems of reversals while still
demonstrating the impact of the independent
variable
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Multiple baseline design
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Changing criterion designs
• Progressively change the level of the
target behaviour required for
reinforcement
• Track changes relative to the criterion
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Changing Criterion Design
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Readings
Concise Overview:
• Leslie & O’Reilly Behaviour Analysis:
foundations and applications to
psychology 1999. Chapter 8
More detail:
• Cooper,J; Heron,T; Heward,B; Applied
Behaviour Analysis 2007 2nd Edition
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