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

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

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

Reversal Design (ABA)

Reversal Design (ABAB)

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)

Irreversibility (suspected)

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

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)

Multiple Baseline Design (Apparent Generalization)

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

Multiple Baseline (generalization) All of the designs we covered today aren’t mutually exclusive - components of different designs can be used in combinations. For example, if you encounter one of the limitations of a multiple BL - generalization across baselines / behaviors - then the original design isn’t providing experimental control. So, under those conditions, you might need to switch designs to demo experimental control. What could you do in this case to show control?

Multiple Baseline ∆ into Reversal Reversing back to BL at least allows you to show an effect on the first BL.

Reversal (irreversibility)

Reversal ∆ into Multiple BL across Subjects