Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.1
Chapter 11: Single-Subject Experimental Research
Objectives Describe the characteristics of a
single-subject design, and explain the benefits and challenges of this type of data collection.
Differentiate among the three major categories of single-subject designs — A–B–A withdrawal, multiple-baseline, and alternating treatments designs — and the variants within each category.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.2
Chapter 11: Single-Subject Experimental Research
Objectives Briefly describe three types of
replication involved in single-subject research, and explain why replication is more useful than statistical analysis.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.3
Single-Subject Experimental Designs
Single-subject (single-case experimental) designs are applied when the sample size is one or when a number of individuals are considered to be one group.
These designs are used to study behavior change in response to treatment.
Each participant serves as his/her own control.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.4
Single-Subject Experimental Designs
Each participant is exposed to both treatment and control phases and is measured during each phase.
Single-subject designs are often used for research and treatment decisions in special education, communication science disorders, and clinical psychology.
Applications of these designs, however, are appropriate to many additional areas.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.5
Single-Subject Experimental Designs
Design representation in single-subject research. The nontreatment phase is
represented by A. The treatment phase is represented
by B. Treatment itself is represented by X Observations are represented by O
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.6
Single-Subject Experimental Designs
For example, if we were to study the in-class swearing behavior of Melissa, we could make several observations of her in class, recording her swearing behavior, introduce an intervention for several classes and observe her swearing behavior, stop the intervention and observe her for several classes. This would be represented as A-B-A.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.7
Single-Subject Experimental Designs
When research results are intended to generalize to other groups, single subject designs are not appropriate.
Sometimes, when it may not be ethical to conduct a group design, a single-subject design is appropriate.
Single-subject designs are appropriate when the aim is to improve functioning of an individual.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.8
Single-Subject Experimental Designs
Internal validity Repeated and reliable measurement
Baseline is established in single-subject designs through multiple observations.
This helps to control for maturation. Data are also collected during the
treatment phases in single-subject designs.
This helps to control for history.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.9
Single-Subject Experimental Designs
Internal validity Instrumentation is a threat to internal
validity in single-subject designs. Intra-observer reliability and inter-
observer reliability are critical for effective single-subject studies.
Treatment should be explained in enough detail to allow for you to do this again with someone else.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.10
Single-Subject Experimental Designs
Internal validity Baseline stability
It is often difficult to know how many data points are necessary for baseline. This is a critical decision in single-subject designs.
Minimum of three data points are required but more are often necessary
Length of the treatment phase parallels baseline Single-variable rule
Only one variable at a time should be manipulated.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.11
Types of Single-Subject Designs
A-B-A withdrawal designs alter phases of baseline and treatment.
There are a number of variations of A-B-A designs. A-B designs
OOOO XOXOXOXO
Baseline Phase Treatment Phase A B
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.12
Types of Single-Subject Designs Additive designs A-B-A Design
OOOO XOXOXOXO OOOOBaseline Phase Treatment Phase Baseline Phase
A B A
Changing criterion design Baseline is followed by successive treatment phases
where in each a more stringent criterion is required.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.13
Example ABA Design
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.14
Types of Single-Subject Designs
A-B-A-B Design
OOOO XOXOXOXO OOOO XOXOXOXO Baseline Phase Treatment Phase Baseline Phase
Treatment Phase A B A B
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.15
Types of Single-Subject Designs
Multiple-Baseline Designs Multiple-baseline designs entail the
systematic addition of behaviors, subjects, or settings for intervention.
Multiple behaviors for one subject One behavior for several subjects One behavior and one subject for several
settings Multiple-baseline designs can often be
used when it is not ethical to remove a treatment or to reverse a treatment.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.16
Data Analysis and Interpretation
Data analysis in single-subject research is typically based on visual inspection and analysis of a graphic representation of results. First, the researcher evaluates the adequacy
of the design. Second, if the design is deemed valid, the
researcher assesses treatment effectiveness. Effectiveness is evaluated based upon clinical
effectiveness not statistical effectiveness.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.17
Data Analysis and Interpretation
Although available, inferential statistical procedures are not often used in single-subject designs.
Educational Research: Competencies for Analysis and Application, 9th edition.Gay, Mills, & Airasian
© 2009 Pearson Education, Inc.All rights reserved.18
Practical Use: Single Subject Design To determine if a client has benefited
from treatment. To determine if a client is done with
treatment. To communicate treatment efficacy to
others involved with this case. To communicate treatment efficacy to
others working with similar cases (careful with generalization)