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Experimental Design

Experimental Design. Dependent variable (DV): Variable observed to determine the effects of an experimental manipulation (behavior) Independent variable (IV): Variable manipulated by the experimenter (environmental event or treatment)

elizabeth-kirk
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Experimental Design

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  1. Experimental Design • Dependent variable (DV): Variable observed to determine the effects of an experimental manipulation (behavior) • Independent variable (IV): Variable manipulated by the experimenter (environmental event or treatment) • Confounding variable: Source of influence other than the IV that may produce changes in the DV • Experimental design: Rules for applying an IV so as to examine its effects on a DV • Functional relation: A relationship in which changes in one variable (DV) are demonstrated to be the result (a function) of changes in another variable (IV) • Single subject design: An experimental design in which a functional relationship can be demonstrated with the behavior of only one subject • Baseline: Condition in effect prior to introduction of the IV • A-B notation system: “A” denotes baseline; subsequent letters (“B,” “C,” etc.) denote different IVs • Replication: Duplication of earlier conditions in an experiment

  2. A-B Design Definition: Single introduction of at least one IV on at least one baseline

  3. A-B Design • Definition: Single introduction of at least one IV on at least one baseline • Advantage: Repeated measurement under BL (A) and Rx (B) conditions allows examination of changes in level, trend, and variability • Limitations: • No replication • Therefore, does not rule out the influence of confounding variables • Therefore, no demonstration of a functional relation

  4. Reversal Design (ABA) Definition: Introduction and subsequent removal of at least one IV on one BL

  5. Reversal Design • Definition: Introduction and subsequent removal of at least one IV on one BL • Variations: ABAB, ABA, BAB, ABAC, etc. • Advantage: Simple yet powerful demonstration of experimental control

  6. Reversal Design (ABAB)

  7. Reversal Design • Definition: Introduction and subsequent removal of at least one IV on one BL • Variations: ABAB, ABA, BAB, ABAC, etc. • Advantage: Simple yet powerful demonstration of experimental control • Limitations: • Detrimental effects of reversal: Ethical considerations • Irreversibility: Failure to reproduce effect observed in a previous phase even though conditions are arranged identically • Sequence/Order effect: Influence of a previous manipulation on responding in a later condition (e.g., training  contingencies)

  8. Irreversibility (suspected)

  9. Multiple Baseline Design Definition: Sequential introduction of an IV across more than one BL

  10. Multiple Baseline Design • Definition: Sequential introduction of an IV across more than one BL • Variations: Across subjects, behaviors, settings • Advantage: Does not require reversal to show experimental control • Disadvantages: • Stability requirement more cumbersome than with a reversal design • Potential generalization across baselines (more likely with MBL across behaviors or settings)

  11. Multiple Baseline Design (Apparent Generalization)

  12. Multielement Design Definition: Rapid alternation of BL and IV conditions (or 2 or more IVs) on a single BL

  13. Multielement Design(aka Alternating Treatments) • Definition: Rapid alternation of BL and IV conditions (or 2 or more IVs) on a single BL • Variations: BL vs. Rx, Rx1 vs. Rx2 (with or without BL), etc. • Advantages: • Does not require baseline (although preferred) • Accommodates trends and instability • Minimizes sequence effects (limited exposure to one condition) • Ideally suited to complex analyses (parametric, component, comparative) • Limitation: Multiple treatment interference

  14. Multielement Design (Adv & Disadv)

  15. Changing Criterion Design Definition: Introduction of one IV on a single BL in step-wise fashion, with steps corresponding to progressive changes in either response requirement or value of the IV

  16. Changing Criterion Design • Definition: Introduction of one IV on a single BL in step-wise fashion, with steps corresponding to progressive changes in either response requirement or value of the IV • Advantage: No reversal and no additional baselines required to show experimental control • Disadvantages: • Requires control over both direction and level of change • Requires careful selection of criterion change

  17. Changing Criterion Design (Problems)

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