Outline
1. Definition
a. Case Studies
b. N=1 Studies
2. Advantages of Case Study approach
3. Disadvantages of Case Study approach
4. Examples of Case Study approach
Case
Definition
• Single-subject studies
are those in which the
focus is on the
performance of
individual subjects
rather than groups of
subjects.
• Even when more than
one subject is studied in
a single-subject design,
data are analyzed one
subject at a time (hence
the name).
Case
Two kinds of single-subject studies
• Case studies
• N=1 studies
• intensive description and
analysis of the
performance of one
subject.
• independent variable is
manipulated within an
individual. (This is an
experiment.)
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Case Studies - advantages
• Focusing on big effects
• in group studies with very
large n, even trivial effects
may be statistically
significant.
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Case Studies - advantages
• Focusing on big effects
• Focusing on individual
performance
• sometimes, averages distort
– that is, no individual’s
performance may be
qualitatively like the
average.
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Case Studies - advantages
• Focusing on big effects
• Focusing on individual
performance
• Reducing ethical problems
• if a treatment has bad sideeffects, harm is minimized.
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Case Studies - advantages
• Focusing on big effects
• Focusing on individual
performance
• Reducing ethical problems
• Breeding hypotheses
• Case studies are a breeding
ground for hypotheses in
research areas about which
little is known
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Case Studies - advantages
• Opportunity for clinical
innovation
• tailor treatment to a
particular patient’s
circumstances and
symptoms
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Case Studies - advantages
• Opportunity for clinical
innovation
• Study rare phenomena
• E.g., “wild boy of Aveyron,”
(R. Shattuck, 1994) – How
are we different from
animals? How do we learn
language? What is
“natural?”
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Case Studies - advantages
• Opportunity for clinical
innovation
• Study rare phenomena
• Challenge theoretical
assumptions
• providing a “counterinstance” – a single case
that violates a universallyaccepted idea.
• E.g., Genie data tested
critical period hypothesis.
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Case Studies - advantages
• Opportunity for clinical
innovation
• Study rare phenomena
• Challenge theoretical
assumptions
• Tentative support for a
theory
• E.g., patient HM – taken as
supporting Atkinson &
Shiffrin’s (1968) model of
memory
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Case Studies - advantages
• Opportunity for clinical
innovation
• Study rare phenomena
• Challenge theoretical
assumptions
• Tentative support for a
theory
• Complements nomothetic
study of behavior
• Allport: clinician wants to
know what a given person
may do, not what people do
“on average”
• idiographic approach (study
of an individual) yields
details that may lead to new
ideas about behavior.
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Case Studies - disadvantages
• Difficulty of drawing causeeffect conclusions
• case studies usually do not
control extraneous
variables.
• e.g., if a patient improves,
was remission
spontaneous? Was it the
treatment, or the attention?
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Case Studies - disadvantages
• Difficulty of drawing causeeffect conclusions
• Possible bias in data
collection
• does patient give selfreports? Are they true?
• are data based on memory?
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Case Studies - disadvantages
• Difficulty of drawing causeeffect conclusions
• Possible bias in data
collection
• Possible bias in interpreting
data if researcher is both
therapist & observer.
• is ‘effect’ of treatment a
matter of therapist’s
impressions?
• does researcher have a lot
invested professionally or
emotionally in the success
of the approach being
studied?
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Case Studies - disadvantages
• depends upon variability in
population
• e.g., for vision research –
little problem
• for personality research –
potentially a big problem
• Note: even data that cannot
be generalized widely may
have a role in theory testing
(see Stanovich).
• Difficulty of drawing causeeffect conclusions
• Possible bias in data
collection
• Possible bias in interpreting
data if researcher is both
therapist & observer.
• Problem of generalizing
from one individual
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Case Studies – some examples
• Sigmund Freud
• argued that in order to have
enough information about
patient to do any good, you
have to do case studies
• you have to work for years
to know patient at all
because the mind is so
complex
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Case Studies –some examples
• Memory patient HM
• bilateral removal of medial
temporal lobe, to relieve
severe epilepsy.
• profoundly amnesic as a
result – capable of little new
(declarative) learning
• cannot extend his digit span
in the normal way
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Case Studies –some examples
• Memory patient HM
• this case very important for
theory of separate Shortterm and Long-term
Memory systems.
• HM thought to have intact
STM, damaged LTM –
cannot get new information
into LTM.
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Case Studies –some examples
• Stevens et al. (Vision
Research, 1976) – Corollary
discharge theory
• Command sent to move
eyes; copy of the command
sent to visual processing
centers.
• Researchers injected
themselves with curare, to
paralyze eye muscles, then
tried to move eyes. Saw
world move in opposite
direction…
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