Small-N and Single-subject Designs

Susan Varni

Fall 2002

Small-N and Single-subject DesignsWhere are we going?

Why Small-N Designs? History of Small-N in Psychology Variations on a Theme Psychophysics

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?

Small-N Designs Definition Studies that use “several” participants with

data that is individually described and may or may not be statistically analyzed

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

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

History of Psychology and Small-N Designs Psychology really began with small-n

Ebbinghaus-nonsense syllables Darwin-child development Watson and Raynor-Little Albert

History of Psychology and Small-N Designs Wilhelm Wundt (1832-1920)

Leipzig Laboratory “E” was the “S” and others were

“replications”

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)

History of Psychology and Small-N Designs

B.F. Skinner Operant

Conditioning Why are we

considering this among small-n designs?

Designs Three Essential Elements

Operational definitions Baselines (A) Treatment (and continued monitoring) (B)

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 }

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

Phantom Limb Results

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5

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1 2 Treatment 3 4

Duration

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

Withdrawal Designs Design (A = baseline, B = treatment)

1. A B A

2. A B A B

3. A B A C

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

Results

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10

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80

1 4 1 4 7 10 3 6

Desire for Cocaine

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

Results

0

0.5

1

1.5

2

2.5

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1 4 6 9 12 15 18 20 25

# condoms

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)

Results

8182838485868788899091

1 2 3 4 5 6 7 8 9 10 11 12 13 14

WeightB C

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

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 treatmentsA-B-A-C-A-D-A A-D-A-C-A-B-A, etc.

And now for something completely different… Although, not really different Exercise

Melody Lateralization Chromatic and luminance modulation

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”