Single Subject Experimental Design

1. Single Subject Experimental Design The Evidence in EBP

2. Evidence-Based Practice (Sackett D et al. 2000) • "Evidence-based medicine is the integration of best research evidence with clinical expertise and patient values."

3. Evidence Based Practice Model • To provide high-quality services • by the integration of: • clinical expertise, • best current evidence, and • client values

4. "evidence is never enough" • the EBP framework acknowledges that the experiences, values, and preferences of ourselves and our patients

5. But still need to deal with it

6. Single Subject Experimental Design Research • Efficacy of Intervention

7. 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

8. 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

9. A-B Design • Phase A - Baseline • Phase B - Intervention

10. Problem with A-B Design • Does not allow the evidence to rule out the threats to internal validity

11. 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)

12. ABA Design • ABA design superior to AB design • Demonstrates experimental control through introducing and withdrawing intervention

13. Potential Problems - ABA Design • Design not common due to: • ethical issues • behavior not subject to changes on withdrawal

14. 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

15. 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

16. 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

17. Multiple Baseline Design • Intervention is introduced sequentially across multiple baselines: • Behaviors • Settings • Subjects

18. Experimental Control in MBD • comes with replication of intervention effects on another behavior (or subject), not a reversal or withdrawal of intervention

19. How to Study Efficiency • Comparison of at least 2 effective treatment interventions, in terms of one more criteria: time, cost, error rate

20. Alternating Treatment Design • Comparison of 2 or more conditions

21. ATD – Appropriate for effectiveness? Make sure to control for order effects

22. 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

23. 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 ?

24. Purposes of Single-Subject Designs* • Does this treatment work? • Which treatment is better? • What parts of a intervention package are doing the job? • Does changing the criterion for success lead to improved performance? • Lubinsky (2004)