Single Subject Design

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Single Subject Design

• Psyc 3000
• John Stanton

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Single subject design defined

• Objective 1 Be able to describe what a single
  subject research design is.
• Single subject research designs use one subject
  at a time to investigate the effects of a
  particular independent variable (treatment).
• Use multiple participants (replications) to
  increase external validity

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Example of SSD
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Characteristics of SSD

• Uses repeated measures
• Need reliable measurement/instrumentation
• Requires a clear description of conditions and
  the DV
• Measurement, IV and DV operationally defined
• 2 general types of phases (could have probes,
  etc.)
• Baseline and treatment conditions

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Phases of SSD

• Objective 2 Be able to list and describe the 2
  phases of a SSD.
• 1. Baseline
• Period of no treatment (reflects natural state)
• Provide standard for evaluating the effect of IV
  and to determine if extraneous variables are
  operating (i.e. the control condition)

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Phases of SSD

• 2. Treatment
• Introduction of the IV
• Phase length should be approximately as long as
  baseline (for comparison purposes)
• Repeated measurement of the DV continues

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General rules for SSD

• Objective3 Know the general rules when using
  single subject designs
• Shouldnt change baseline until
• Little variability
• No trends
• Unless the trend is in the opposite direction of
  expected effect
• Only change one variable at a time

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General rules for SSD

• Length of phase (suggestions)
• Keep all the same length
• Controls for maturation
• To reduce carry over effects use shorter phases
  (treatment)
• Extend phases to include cyclic subject variables
• i.e. menstrual cycle, daily issues

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Types of SSD

• Reversal design
• Alternating treatments design
• Multiple baseline design
• Changing criterion design

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Reversal design

• Objective 4 Know the critical features for the
  reversal design.
• Critical features
• At least 2 conditions
• Baseline
• Treatment
• Same condition present for consecutive sessions
• Conditions dont alternate rapidly
• Types
• AB
• ABA
• ABAB

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AB

• 1 baseline and 1 treatment phase
• Ex. Kid having trouble working on school work
  (i.e. staying on task), the treatment is setting
  up a reinforcement contingency that gives him a
  dollar for every minute he stays on task

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AB
A
B
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AB

• Problems
• Limited control over threats to internal validity
• No control for extraneous variables - that is
  changes in the DV could be caused by numerous
  things

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ABA

• Baseline (A) Treatment (B) Baseline (A)
  (withdrawal)
• The withdrawal strengthens the relationship
  between the IV and DV
• Ex. Kid having trouble working on school work
  (i.e. staying on task), the treatment is setting
  up a reinforcement contingency that gives him a
  dollar for every minute he stays on task

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ABA
A
B
A
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ABA

• Problems
• Doesnt completely control for extraneous
  variables (but more evidence!)
• Irreversibility
• Some IVs cant be withdrawn
• Some behaviors cant be reversed
• Ethical and legal issues
• Sequence effects

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ABAB

• Baseline Treatment Baseline Treatment
• Increases the confidence in the treatment effect
• Better controls for extraneous variables
• Ex. Kid having trouble working on school work
  (i.e. staying on task), the treatment is setting
  up a reinforcement contingency that gives him a
  dollar for every minute he stays on task

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ABAB
A
B
A
B
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ABAB

• Problems
• Irreversibility (same as in ABA)
• Sequence effects

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Alternating treatments

• Objective5 Know the critical features of the
  alternating treatments design.
• Critical features
• 2 or more treatments presented
• Treatment phases are rapidly alternated
• In a pseudo random fashion
• Generally a baseline phase (not required)

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Alternating treatments
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Alternating treatments

• Advantages
• No treatment withdrawal
• Faster comparison of treatments
• Variable data is okay
• Problems
• Artificiality
• Interference between treatment phases
• Treatments must sufficiently differ

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Multiple baseline design

• Objective 6 Know the critical features of the
  multiple baseline design.
• Critical features
• More than one baseline
• recorded during the same time period for
  different lengths of time
• Introduce treatment in one condition at a time
• Sequentially in order of baseline stability
• No withdrawal or reversal
• Avoids any associated problems
• Must have overlap in terms of setting,
  researchers used, participants used, etc. to
  detect potential extraneous variables otherwise
  it is simply a series of stacked AB designs

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Multiple baseline design
Bob
Minutes on Task
Carol
Joe
Sessions
Sessions
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Multiple baseline design

• 3 types
• Across participants
• Same settings and behavior, but different
  participants
• Across behaviors
• Same participant and setting, but different
  behaviors
• Across settings
• Same participants and behavior, but different
  settings

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Across participants
Bob
Homeroom
Minutes on Task
Carol
Homeroom
Joe
Homeroom
Sessions
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Across behaviors
Min. on Task
Homeroom
Bob
Min. In Seat
Homeroom
Min. w/ No Talkouts
Homeroom
Sessions
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Across Settings
Homeroom
Bob
Minutes on Task
Math
Bob
Reading
Bob
Sessions
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Changing criterion design

• Objective 7 Know the critical features of the
  changing criterion design.
• Critical features
• Uses the same, behavior, participant, and setting
• Baseline phase
• Shows experimental control by demonstrating that
  changes in the DV occur only when the criterion
  changes

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Changing criterion design
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Changing criterion design

• Considerations
• Length of phase
• Considerable variation for control purposes
• Size of incremental change
• Considerable variation for control purposes
• of phases
• More better

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Analysis of SSD

• Objective 8 Know how single subject designs are
  most commonly analyzed.
• Visual analysis most common
• Assess trends and levels between adjacent phases
• Level value of DV
• Trend direction of the level of DV
• Increasing, decreasing, stable, variable