chapter 11: single-subject experimental research

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.



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.



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.




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.




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




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.




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.




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.




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.




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.



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



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.



Example ABA Design




A-B-A-B Design

OOOO XOXOXOXO OOOO XOXOXOXO Baseline Phase Treatment Phase Baseline Phase

Treatment Phase A B A B




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.



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.



Data Analysis and Interpretation

Although available, inferential statistical procedures are not often used in single-subject designs.



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)

chapter 11: single-subject experimental research

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