lect 9

Mayer Chapter 9: Basic Experimental Design

SIX COMPONENTS OF EXPERIMENTS IN ABA

1) At least one subject

2) At least one behavior (AKA: dependent variable)

3) At least one setting

4) At least one treatment (AKA: independent variable)

5) A measurement system and ongoing analysis of data

6) An experimental design

SINGLE-SUBJECT EXPERIMENTAL DESIGNS (#1 OF THE 6 COMPONENTS)

• ABA uses single-subject designs. This does not mean that there is only one subject (although sometimes there is only one individual).

• Called SINGLE-SUBJECT because the subject acts as his/her own control.

• Repeated measures of the subject’s behavior during each phase of the study provide the basis for comparing experimental variables as they are presented or withdrawn in the presence and absence of the independent variable.

• The individual is exposed to each condition several times over the course of a study.

• ABA studies usually involve more than one subject (four to eight is common).

• Each subject’s data are graphed separately.

• ABA does not use group comparison designs that are traditionally used in psychology. Masks individual progress.

DEPENDENT VARIABLE (#2 OF THE 6 COMPONENTS)

• Some studies measure more than one dependent variable.

• Reasons for multiple dependent variables include the following:

• Provide data patterns that can serve as controls for evaluating and replicating the effects of an IV.

• Assess if any collateral effects occurred.

• Determine whether changes in the behavior of a person other than the subject occur during the course of an experiment and if such changes can explain changes in the subject’s behavior.

SINGLE SETTING (#3 OF THE 6 COMPONENTS)

• Control two sets of environmental variables to demonstrate experimental control.

• IV (present, withdraw, or vary its value)

• Extraneous variables (prevent unplanned environmental variation)

• In laboratories, we can control environments better, but in applied settings like homes, schools, etc. it is harder to control the environment.

• When unplanned variations take place, you must try to wait them out or incorporate them into the design. Repeated measures of behavior tell us whether unplanned environmental changes are of concern.

INDEPENDENT VARIABLE (#4 OF THE 6 COMPONENTS)

• AKA: Treatment(s), Intervention, Experimental Variable.

• The particular aspect of the environment that the experimenter manipulates to find out whether it affects the subject’s behavior.

A MEASUREMENT SYSTEM AND ONGOING ANALYSIS OF DATA

(#5 OF THE 6 COMPONENTS)

• Observation and recording procedures must be conducted in a standardized manner.

• Standardization involves every aspect of the measurement system (e.g., from the behavior definition to scheduling of observations).

• Behaviorists must detect changes in level, trend, variability.

AN EXPERIMENTAL DESIGN (#6 OF THE 6 COMPONENTS)

• The particular arrangement of conditions in a study so that meaningful comparisons of the effects of the presence, absence, or different values of the IV can be made.

• Important rules of Experimental Design:

• Change only 1 variable at a time.

• Do not get locked into textbook designs – select and combine designs that best fit the research question.

TYPES OF SINGLE-SUBJECT DESIGNS

• Withdrawal (Return to Baseline) Design

• Reversal Design

• Multiple Baseline Design

• Changing Criterion

• Alternating Treatments

WITHDRAWAL DESIGN

• Involves the removal of the intervention to test its effect.

• Used to determine whether the effect of the intervention can be reproduced.

• Involves:

• Obtaining a base rate measure of the target behavior

• Repeatedly applying the intervention or procedure

• Withdrawing the intervention for a time, under the same conditions as those that were in effect during the baseline period

• Reapplying the intervention.

REVERSAL DESIGN

• Design in which the researcher REVERSES responding to a level obtained in the previous condition.

• The independent variable is withdrawn (A-B-A-B) or reversed in its focus (e.g., DRI/DRA).

• Alternation between baseline and a particular intervention

• Each reversal in the design strengthens the experimental control, which helps demonstrate function.

• Functional relation is strengthened with each reversal (e.g., switch from one (1) condition to the other with a corresponding change in trend and level).

• The behavior must approximate the initial baseline level.

• Requires at least (3) consecutive phases:

• Initial Baseline (A)

• Intervention (B)

• Return to Baseline (A)

• A-B-A-B preferred over A-B-A as a stronger design

MULTIPLE BASELINE DESIGN

• Most widely used design

• Highly flexible

• Staggered implementation of the intervention in a step-wise fashion across behaviors, settings, and subjects.

• Do not have to withdraw a treatment variable in this design.

MULTIPLE BASELINE ACROSS BEHAVIORS

• Two or more different behaviors of the SAME subject.

• Each subject serves as his/her own control.

• After steady state baseline responding, the IV is applied to the first behavior, while other behaviors are kept in baseline.

• When steady state responding is reached for the first behavior, then the IV is applied to the next behavior.

MULTIPLE BASELINE ACROSS SETTINGS

• A single behavior is targeted in two or more different settings or conditions.

• After steady state baseline responding, the independent variable is applied to the first setting, while other settings are kept in baseline.

• When steady state responding is reached for the first setting, then the IV is applied to the next setting.

MULTIPLE BASELINE ACROSS SUBJECTS

• One target behavior for two or more subjects in the same setting.

• After steady state responding, the independent variable is applied to the first subject, while other subjects are kept in baseline.

• When steady state responding is reached for the first subject, then the IV is applied to the next subject.

• Most widely used multiple baseline design.

TWO VARIATIONS OF A MULTIPLE BASELINE DESIGN

(1) Multiple Probe Design • Analyzes relations between the

Independent Variable and acquisition of skill sequences.

• Instead of simultaneous baselines, probes provide the basis for determining if the behavior change has occurred prior to intervention.

• (2) Delayed Multiple Baseline Design

• Initial baseline and intervention begin and subsequent baselines are added in a delayed or staggered fashion.

• Effective when:

• reversal design is not possible

• limited resources preclude a full-scale design

• when a new behavior, subject, or setting becomes available).

• Limitations: Shorter Baselines do not show interdependence of DVs.

CHANGING CRITERION

• Experimental design in which an initial baseline phase is followed by a series of treatment phases consisting of successive and gradually changing criteria for reinforcement or punishment.

• There is only ONE behavior in this design.

• Behavior in this design has to already be in the subject’s repertoire.

• Evaluates treatment that is applied in a graduated or step-wise fashion.

• Technically, it is a variation of the multiple baseline design.

ALTERNATING TREATMENT

DESIGN

• AKA: Simultaneous treatments design, concurrent schedules design, alternating treatments design, multi-element baseline design, multi-element design, multiple schedules design.

• An experimental design in which two or more conditions are presented in rapidly alternating succession independent of the level of responding and the differential effects on the target behavior are noted.

• Compares two or more independent variables to one another to see which independent variable would be best to utilize with the client.

• Based on stimulus discrimination (each independent variable has an obvious SD signaling which independent variable is in effect at any given time.

• For each independent variable, data are plotted separately on the same graph.

• Independent variables may be:

• Alternated across daily sessions.

• Given in sessions occurring the same day.

• Implemented during each portion of the same session.

SINGLE PHASE WITHOUT BASELINE : DOES NOT REQUIRE

AN INITIAL BASELINE.

WITH BASELINE AND FINAL BEST TREATMENT PHASE : MOST WIDELY USED.

3 VARIATIONS OF ALTERNATING TREATMENT DESIGNS

WITH BASELINE : WHENEVER POSSIBLE, BASELINE SHOULD BE CONDUCTED AS IT

SHOWS THE CHANGE PRODUCED BY EACH TREATMENT COMPARED TO THE NATURAL

LEVEL OF PERFORMANCE WITHOUT AN INTERVENTION.