I’m feeling blue,
how bout you?
Me too!
Chapter 12
Within-subjects
for the Small N design
We’ll take over the world one
small N design at a time
Music to
my ears
1
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
2
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 eugenics.
Subject(s): FISHER, Ronald
Source: Natural History, Dec91, Vol. 100 Issue 12,
p8, 7p
Author(s): Gould, S.J.
Should we - can we - take a kindly view
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
3
arguments; Details.
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.
Subject 1
Subject 2
Combined
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4
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3
2
2
1
1
0
0
7
3
2
1
1
2
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1
2
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0
1
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44
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?
5
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 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
6
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
7
Small N Designs
Popular in:
• Clinical and animal research
• Laboratory and field studies
• Psychophysics
• Studies of learning
• Used most extensively in operant
conditioning research
8
9
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
10
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)
11
Variations of the ABA Design
A Swedish
design that
only made
sense in the
drug-induced
haze of the
70s disco era.
12
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?
13
Variations of the ABA Design
AC/DC – a.k.a, the “Indiscrete trials design”
• After “A”, never
return to baseline
• skip all the boring B
condition stuff and
go right for the CDC
conditions that put
you on a fast track to
the land down-under
(where they’re from)…
• Apply thunderbolt
between C and D.
14
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
A
B
A
Baseline
Experimental
Baseline
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