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for comparing experimental variables as they are presented or withdrawn in the presence and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.