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Small-N and Single-subject Designs
Susan VarniFall 2002
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Small-N and Single-subject DesignsWhere are we going? Why Small-N Designs? History of Small-N in Psychology Variations on a Theme Psychophysics
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Why Are You Studying Psychology? Take 2 minutes to write down why you are
studying psychology. What about psychology interests you? What topics? What profession do you aspire to? What impassions you about psychology? What do you hope to do with the
knowledge that you gain here?
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Small-N Designs Definition Studies that use “several” participants with
data that is individually described and may or may not be statistically analyzed
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Pros of Small-N Avoiding problems with the group mean* Can examine participants from hard to find populations*
*Key reasons currently! Following are both current & historical reasons
Can deal explicitly with individual (not group) behavior Results are easy to interpret (often no stats!) Avoids small, unimportant effects Flexibility Can focus on helping one (few) participant
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Cons of Small-N Hard to demonstrate causality No controls in most cases Lack of statistics
(Major “significance test” is the IOT) Can’t really look at interaction effects Counterbalancing is a problem DV usually limited to response rates Problem of external validity
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History of Psychology and Small-N Designs Psychology really began with small-n
Ebbinghaus-nonsense syllables Darwin-child development Watson and Raynor-Little Albert
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History of Psychology and Small-N Designs Wilhelm Wundt (1832-1920)
Leipzig Laboratory “E” was the “S” and others were
“replications”
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History of Psychology and Small-N Designs Edward Thorndike (1874-1949)
Animal Learning“I then suggested [to James] experiments with the instinctive and intelligent behavior of chicken as a topic, and this was accepted. I kept these animals and conducted the experiments in my room until the landlady’s protests were imperative. James tried to get the few square feet required for me in the laboratory…He was refused and with his habitual kindness and devotion to underdogs and eccentric aspects of science, harbored my chickens in the cellar of his own home for the rest of the year” (Thorndike, 1936 as quoted in Hothersall, 1995)
Cats and Puzzle Boxes (results for every cat)
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History of Psychology and Small-N Designs
B.F. Skinner Operant
Conditioning Why are we
considering this among small-n designs?
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Designs Three Essential Elements
Operational definitions Baselines (A) Treatment (and continued monitoring) (B)
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Baseline Designs Once baseline has been maintained, it is
unlikely that a confounding event will affect results on the same trial as the manipulation
Design (A = baseline, B = treatment)A B
{ O1 X/O2 }
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Phantom Pain (A-B) Jonsson & Fisher, 1996 Phantom pain is hard to treat (don’t really
understand it) and methods have been inconsistent
Hard to find participants Studied one woman who has had both legs
amputated Treated pain control by attention diversion
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Phantom Limb Results
0
5
10
15
20
25
1 2 Treatment 3 4
Duration
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Withdrawal Designs It is unlikely that a confound will cease to
affect the results on the same trial the manipulation is removed
It is more unlikely that a confound will re-affect the results on the same trial the manipulation is re-introduced
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Withdrawal Designs Design (A = baseline, B = treatment)
1. A B A
2. A B A B
3. A B A C
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Cocaine Abstinence (A-B-A) Silverman, Wong et al., 1998 Methods of keeping people in a methodone
treatment program from using cocaine Used escalating reinforcement for cocaine-free
urine samples ($2.50 for first, add $2.96 for each additional) (could get up to $1950 over the course of the study)
Baseline, reinforcement, then removed reinforcement
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Results
0
1020
30
40
5060
70
80
1 4 1 4 7 10 3 6
Desire for Cocaine
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Condom Taking (A-B-A-B) Kirby et al., 1998 Drug abusers are at high-risk for HIV Would prompting cocaine users result in
their taking (and hopefully using) more condoms?
Treatment: After counseling, clients were informed of risk and encouraged to take condoms
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Results
00.5
11.5
22.5
33.5
44.5
1 4 6 9 12 15 18 20 25
# condoms
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Conversion Disorder (A-B-(AA)-C) Donahue, Thevenin, & Runyon, 1997 Conversion disorder: physical symptoms (often
following stressor) without organic cause 12-year old girl complained of throat constriction
(following choking on food) Treated with (B) training meals (positive thoughts
while eating), and then with (C) reinforcement (call brother, eat w/TV)
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Results
8182838485868788899091
1 2 3 4 5 6 7 8 9 10 11 12 13 14
WeightB C
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Multiple Baseline Designs If treatment start time is staggered, it is unlikely a
single confound can explain all perceived treatment effects
3 Types Same behavior in 2 or more individuals 2 or more different behaviors within the same
individual Same behavior within the same individual but in 2 or
more different settings
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Other Designs Mentioned in the Text Changing criterion design (“shaping”) A - B - C - B, where C is non-contingent reinf. A - A1 - B - A1 - B (A1 a placebo for B) Alternating treatments
A-B-A-C-A-D-A A-D-A-C-A-B-A, etc.
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And now for something completely different… Although, not really different Exercise
Melody Lateralization Chromatic and luminance modulation
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Psychophysics Fechner, October 22, 1850 Elements of Psychophysics
(1860) Profound insight about relation of physical stimuli () to
their mental representations () Concepts:
Absolute threshold (min. energy to detect) Difference threshold (min. energy to notice change)
Methods (limits, constant stimuli, adjustment) are still in use Newer -- signal detection theory (SDT) separates our
sensitivity to stimuli from individual criteria for saying “yes” or “no”