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Chapter 12Within-subjects

for the Small N design

I’m feeling blue, how bout you?

We’ll take over the world one small N design at a time

Me too!

Music to my ears

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Large and Small N designs

Small N

• one or a few subjects

Large N

• Greater than a few subjects (often multiple groups)

• most common technique used in research design

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Large N Designs

• Gained in popularity after Sir Ronald Fisher invented the analysis of variance in the 1930s

• Easier to generalize with more than one subject (greater external validity)

Title: The smoking gun of eugenicsThe smoking gun of eugenics.Subject(s): FISHER, RonaldSource: Natural History, Dec91, Vol. 100 Issue 12, p8, 7pAuthor(s): Gould, S.J.

Should we - can we - take a kindly view Should we - can we - take a kindly view toward a hero's faults?toward a hero's faults?

Details two key errors in the works of evolutionary biologist Sir Ronald Aylmer Fisher concerning the correlation/causality between smoking and lung cancer and the notion that advanced civilizations destroy themselves because their upper classes become genetically infertile, causing society to weaken and crumble. Logical but biased arguments; `The Genetical Theory of Natural Selection'; Serious consequences of such arguments; Details.

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Why even use small N?

• Precision – pooling or combining data can obscure the results of individual subjects

• You may miss effects by pooling data across individuals.

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Subject 1 Subject 2 Combined

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Why even use small N?

• Another example where pooling data led to a misinterpretation of what subjects had or had not learned?

• Hint: a series of water maze studies on the effects of partial reinforcement (PR)– How many subjects in the PR group?– What data was pooled?– What was discovered by de-aggregating the

data?– What’s the big picture lesson?

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The BIG PICTURE lesson• Large N’s aggregate over subjects.• Smaller N studies sometimes aggregate over

time.• Both have the potential to loose fidelity

Mirriam-Webster OnlineMirriam-Webster Online

a: the quality or state of being faithful b: accuracy in details : exactness 2: the degree to which an electronic device (as a record player, radio, or television) accurately reproduces its effect (as sound or picture)

From Wikipedia, the free encyclopedia

High fidelity (disambiguation)

High fidelity or hi-fi is most commonly a term for the high-quality reproduction of sound or images

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Small N Designs

• Also used for practical reasons– Only a few patients in clinical research for a

rare disease, plenty with common ones– Animals may be expensive (especially those fancy rats)

Just the crowd I want to hang

around and get advice from

…ideal for poor researchers with restricted or limited access to human patients and/or

…those that lack motivation to collect acceptable amounts of data for a large N study

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Small N Designs

Popular in:• Clinical and animal research• Laboratory and field studies• Psychophysics• Studies of learning

• Used most extensively in operant conditioning research

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ABA Design

• The return to baseline in the ABA design tests whether B had an effect or whether another extraneous variable confounded the study.

• Thus, the effect of B, the experimental treatment, must be reversible

• it is also called a reversal design

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Variations of the ABA Design

• ABABA – two treatments and two returns to baseline – can detect cumulative effects of the treatment

• ABACADA – multiple experimental conditions - B, C and D represent different treatments

• AB design – sacrifice the return to baseline if it would harm the subject (e.g., behavior modification worked in reducing self-injurious behavior)

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Variations of the ABA Design

A Swedish A Swedish design that design that only made only made sense in the sense in the drug-induced drug-induced haze of the haze of the 70s disco era.70s disco era.

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Variations of the ABA Design

• Multiple baseline design – a series of baselines and treatments are compared, but once a treatment is established it is not withdrawn (e.g. AAABBB no more As)

• Discrete trials design – does not rely on baselines at all, but compares performance across treatment conditions (e.g. BCDE) a BC design would be analogous to what large N design?

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Variations of the ABA Design

• After “A”, never After “A”, never return to baseline return to baseline

• skip all the boring B skip all the boring B condition stuff and condition stuff and go right for the CDC go right for the CDC conditions that put conditions that put you on a fast track to you on a fast track to the land down-under the land down-under (where they’re from)(where they’re from)……

• Apply thunderbolt Apply thunderbolt between C and D.between C and D.

AC/DC – a.k.a, the “Indiscrete trials design”

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B. F. Skinner

• Studied changes in the rate of behavior (e.g., a rat lever pressing for food)

• by careful, continuous measurement of a single subject over time.

The control and experimental conditions are given to the same subject at different times

ABaseline

BExperimental

ABaseline