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Outline

1. Definitiona. Case Studiesb. N=1 Studies

2. Advantages of Case Study approach3. Disadvantages of Case Study approach4. Examples of Case Study approach

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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).

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Two kinds of single-subject studies

• Case studies• intensive description and

analysis of the performance of one subject.

• N=1 studies• 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 side-effects, 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 “counter-instance” – a single case that violates a universally-accepted 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 cause-effect 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 cause-effect conclusions

• Possible bias in data collection

• does patient give self-reports? Are they true?

• are data based on memory?

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Case Studies - disadvantages

• Difficulty of drawing cause-effect 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

• Difficulty of drawing cause-effect conclusions

• Possible bias in data collection

• Possible bias in interpreting data if researcher is both therapist & observer.

• Problem of generalizing from one individual

• 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).

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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 Short-term 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…