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Single Subject Experimental Design

The Evidence in EBP

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Evidence-Based Practice (Sackett D et al. 2000)

• "Evidence-based medicine is the integration of best research evidence with clinical expertise and patient values."

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Evidence Based Practice Model

• To provide high-quality services

• by the integration of: – clinical expertise, – best current evidence,

and – client values

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"evidence is never enough"

• the EBP framework acknowledges that the experiences, values, and preferences of ourselves and our patients

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But still need to deal with it

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Single Subject Experimental Design Research

• Efficacy of Intervention

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Efficacy encompasses

• Effectiveness– Behavior change as a direct result of

intervention

• Efficiency– Comparison of at least 2 effective treatment

interventions, in terms of one more criteria: time, cost, error rate

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Designs in Single-Subject Studies

• Phases– A phase – baseline– B phase – condition

• 2 Types of SSD– Descriptive

• A: Baseline only• B: Intervention only• A-B: Baseline-Intervention

– Experimental (control)• Examine cause-effect relationship

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A-B Design

• Phase A - Baseline• Phase B - Intervention

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Problem with A-B Design

• Does not allow the evidence to rule out the threats to internal validity

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Internal Validity

• Did in fact the experimental conditions make a difference in this specific instance?

• Threats to internal validity– Maturation/recovery– History (previous intervention)– Hawthorne Effect (testing effect)

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ABA Design• ABA design superior

to AB design• Demonstrates

experimental control through introducing and withdrawing intervention

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Potential Problems - ABA Design

• Design not common due to: – ethical issues– behavior not subject to

changes on withdrawal

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Reversal Design is applied when?

• Removal of experimental contingencies does not result in a return back to baseline

• Reversal is the application of experimental contingencies to an alternate behavior incompatible with the target behavior

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ABAB Design – Example 1

• Solves ethical issue• Vaugh & Horner (1995)

– Effects of concrete (symbol + spoken words) versus verbal modes for choice making

– A: meal choices – verbal– B: choices – picture + verbal– Resulted in more

acceptances with B phase

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ABAB Design – Example 2

• Rotholz et al (1989)– 2 communication modes

for requesting fast food– A- Choices w/ sign

language– B – Graphic symbols– Results use of graphic

symbols resulted in more successful requests than signing in community settings

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Multiple Baseline Design• Intervention is

introduced sequentially across multiple baselines:– Behaviors– Settings– Subjects

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Experimental Control in MBD

• comes with replication of intervention effects on another behavior (or subject), not a reversal or withdrawal of intervention

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How to Study Efficiency

– Comparison of at least 2 effective treatment interventions, in terms of one more criteria: time, cost, error rate

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Alternating Treatment Design• Comparison of 2 or more conditions

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ATD – Appropriate for effectiveness?

Make sure to control for order effects

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Order Effects • PRESENTATION ORDER OF ITEMS

• 1-2-3 camel-bat-seal• 1-3-2 camel-seal-bat• 2-3-1 bat-seal-camel• 2-1-3 bat-camel-seal• 3-1-2 seal-camel-bat• 3-2-1 seal-bat-camel

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External Validity

• Generalization -- The degree to which the results of a research study or experiment can be generalized to other groups, settings or situations.

• Problem for SSD

• Solution ?

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Purposes of Single-Subject Designs*

1. Does this treatment work?

2. Which treatment is better?

3. What parts of a intervention package are doing the job?

4. Does changing the criterion for success lead to improved performance?

• Lubinsky (2004)