Download Single-Case Research

Single-Case Research
Exceptions to Research Findings
• Research findings uncover generalities and
trends averaging across individual differences.
• But, there are always exceptions (outliers)!
• Exceptions do not invalidate research findings,
but should they be ignored?
Different Approaches
Nomothetic approach – aims to establish
general principles and broad generalizations that
apply across individuals.
Idiographic approach – aims to describe,
analyze, and explain the behavior of individuals.
Two types of Single Case Research
Single Case Experiments: manipulate IV’s and
exert experimental control and analyze responses
of an individual participant.
Case Studies: uncontrolled impressionistic
descriptions related to treatment of individual
problems.
Single-Case Experimental Designs
• Unit of analysis is the individual participant
rather than the experimental group in a
condition.
• More than one participant may be studied, but
their responses are analyzed individually
• Cannot analyze these data with inferential
statistics such as t-tests and F-tests
Group Designs vs. Single-case
(1) Error Variance
• Pro-Group design argument:
▫ Averaging across participants provides a more
accurate estimate of a variable’s general effect
▫ Group designs allow us to estimate the amount of
between participant error variance in our data
Group Designs vs. Single-case
• Pro-Single case argument
▫ Error variance is created by averaging over
participants in a group design
 interparticipant variance (between-participant)
▫ Researchers using group designs ignore the ―real‖
error variance within the participant.
 This intraparticipant variance is more important to
understand.
Group Designs vs. Single-case
(2) Generalizability
• Group design argument – averaging the
scores of several participants reduces the
distinct responses of distinct participants to
show the general effect.
• Single-case argument – averaging responses
may not accurately describe any particular
participant’s responses.
Group Designs vs. Single-case Designs
(3) Reliability
• Group design– reliability established by replicating
studies
• Single-case argument – reliability established via:
▫ Intraparticipant replication – replicating the effects of
the IV with a single participant
▫ Interparticipant replication – seeing whether the effects
obtained for one participant generalize to other participants
in the same study
Pro-Single Case Example:
Learning Curves
An Individual Participant
Averaging Across Participants
60
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0
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T1 T2 T3 T4 T5 T6
Trials
T1 T2 T3 T4 T5 T6
Trials
ABA Designs:
IV’s for Single-case experiments
• ABA Design (reversal designs)
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▫
▫
▫
▫
Behavior is measured (Baseline period; A)
Independent variable is introduced (B)
Behavior is measured
Independent variable is removed (A)
Behavior is measured
ABAB Designs
• Introduce IV a second time to show continued impact
(Deitz, 1977)
Baseline
Treatment1
Reversal
Treatment 2
Frequency of Talking Aloud
40
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0
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Sessions
21 23 25 27 29 31
33 35
Multiple Baseline Designs
• Two or more behaviors studied simultaneously
▫ Obtain baseline on all behaviors
▫ Introduce an independent variable that is
supposed to affect only one behavior
• Shows that the IV is causing the target behavior
to change and is not affecting the other
behaviors.
Data from Single-Participant Designs
• Results are typically shown in graphs
• Graphic analysis – researcher visually
inspects the graph of the individual participant
to see if the independent variable had an effect
• Criticized for having no explicit criteria for
deciding when an effect significant
Graphic Analysis: ABA design
Baseline
Treatment
Baseline
Baseline
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5
5
0
Treatment
Baseline
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
Since we can’t use inferential statistics, there is no
objective way to say if there is an effect on the left
or right graph.
Uses of Single-Case Experimental Designs
• Operant conditioning: schedules of reinforcement
and punishment
• Psychophysiological processes: effects of drugs
• Behavior modification: techniques for changing
problem behaviors based on operant conditioning
• Demonstrational purposes
Critique of Single-Participant Designs
Effects are not necessarily generalizable
▫ Individual participants may not be representative
of the population at large
Neglect of interactions among variables
Ethical issues
▫ Example: Do you withdraw an effective treatment
from a particularly troubled client in a reversal
design?
Two types of Single Case Research
Single Case Experiments: manipulate IV’s and
exert experimental control and analyze responses
of an individual participant.
Case Studies: impressionistic descriptions
related to treatment of individual problems with
no experimental control.
Case Study
Case study: a detailed study of a single individual,
group, or event
Use of numerous sources: observation, interviews,
questionnaires, news reports, and archival records
Information is compiled into a narrative
description
Uses of the Case Study Method
• Describe rare phenomena
• Psychobiography: using psychology theory to
understand famous people (Janis, groupthink)
• Illustrative anecdotes
• Source of Insight and Ideas
Case Studies
• Heaven’s Gate Cult and cognitive
dissonance
• Bay of Pigs fiasco and groupthink
• H.M and modular memory
Heaven’s Gate Cult
Karian Keech receives ―automatic writing‖ from
alien planet Clarion that floods will engulf Earth.
Cult members sell all possessions, leave college
and spouses and jobs to prepare for UFO
deliverance on December 21, 1954, 12:00am.
When no spaceship comes, Karian cries, then just
hours before the flood, another message
indicating that the group’s faith saved the Earth.
Cognitive Dissonance & Belief Disconfirmation
Festinger (1956): Heaven’s Gate cult provided the
first evidence for cognitive dissonance.
Two dissonant cognitions:
1. I gave up everything in my life to be saved by a
UFO from the flood. bolster this belief by proselytizing
2. The UFO and the flood never happened.
What is the easiest way to resolve this dissonance?
Heaven’s Gate Case Study Outcome?
Cognitive dissonance has supported
through 100’s of laboratory experiments
and quasi-experimental studies.
Cognitive dissonance: when behaviors conflict
with thoughts, you support the implications of
behaviors because you are stuck with your
behaviors.
Groupthink: The Bay of Pigs Case
Robert Kennedy: brother of JFK
running the meeting, tells everyone that
the president has already made up his
mind.
Robert Kennedy acts as a mindguard
telling doubters to not bring up their
concerns.
Due to dislike of communism, group
feels they are morally right.
Without open discussion, no options
other than the invasion plan are
discussed.
Result?
Groupthink Case Study Outcome?
Groupthink (Janis, 1972)
• Only ever supported by other case studies of
successes of group decision-making (Cuban Missile
Crisis) and failures (Challenger Disaster).
• Benefits: Focused attention on inaccurate
assumption that groups make better decisions than
individuals  lots of research
• Drawbacks: Non-scientific because cases always
identified AFTER failure or success of decision.
With this approach it is not falsifiable. Unethical
to conduct a controlled experiment in geopolitics.
H.M. Henry Gustav Molaison
Suffered from severe epilepsy which
was treated in 1953 with bi-lateral
removal of the medial temporal lobes
(hippocampus, parahippocampal
gyrus, amygdala).
H.M.
Alleviated epilepsy, but…
Memory deficits
• anterograde amnesia—no new episodic memories
(for events)
• loss of (recent) prior memories
Memory retained
• working memory: current ideas in mind
• procedural memory: old and new motor and other
sequential ―how to do X‖
H.M. Outcome
Notion that certain memory functions are linked
to certain brain regions as separate modules:
episodic memory formation vs. retrieval
procedural and working vs. episodic
Cognitive Neuropsychology: founded based on
this general idea.
Helps us understand both patients with deficits
and normal functioning of memory.
Limitations of the Case Study Approach
• Failure to control extraneous variables
▫ Alternative explanations can not be ruled out
• Observer biases
▫ All observations may be conducted by a single
researcher
▫ No way of determining reliability and validity of these
observations without interparticipant variance.
• Case study ideas should be tested through controlled
experiments, whenever possible.
Come up with your own Case Study
• What individual or group or historic occurrence
will you study that has never been studied?
• What predictor and criterion variables will you
suggest?
• What other events/phenomena will you apply
this to?
• How could you test this in the lab under
controlled conditions, or in a quasi-experiment
in the field?