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Chapter 11: Single-Subject Experimental Research

Educational Research:

Competencies for Analysis and Application

11/E

Geoffrey Mills and Lorraine Gay

Gay & Mills

Educational Research, 11e

11-‹#›

After reading Chapter 11, you should be able to do the following

Describe the major categories of single-subject experimental designs, and explain the benefits and challenges of this type of research.

Describe issues related to data analysis and interpretation in single-subject experimental research.

Discuss threats to validity in single-subject experimental research.

Describe the importance of replication in single-subject experimental research.

Gay & Mills

Educational Research, 11e

11-‹#›

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 as one group.

These designs are used to study behavior change in response to treatment.

Each participant serves as his or her own control.

Gay & Mills

Educational Research, 11e

11-‹#›

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 in special education, communication science disorders, and clinical psychology.

Applications of these designs, however, are appropriate to many additional areas of research.

Single-variable rule

Only one variable at a time should be manipulated in single-subject experimental designs

Gay & Mills

Educational Research, 11e

11-‹#›

Single-Subject Experimental Designs

Design representation in single-subject research.

The nontreatment phase is represented by A.

The treatment phase is represented by B.

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.

Gay & Mills

Educational Research, 11e

11-‹#›

Single-Subject versus Group Designs

Often applied in clinical settings where the emphasis is therapeutic impact.

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.

Gay & Mills

Educational Research, 11e

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

Gay & Mills

Educational Research, 11e

11-‹#›

Types of Single-Subject Designs

Additive designs: Variations of A-B design that involves the additional phases

A-B-A Design

OOOO XOXOXOXO OOOO

Baseline 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.

Gay & Mills

Educational Research, 11e

11-‹#›

Types of Single-Subject Designs

A-B-A-B Design

OOOO XOXOXOXO OOOO XOXOXOXO

Baseline Treatment Baseline Treatment

A B A B

Gay & Mills

Educational Research, 11e

11-‹#›

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.

Gay & Mills

Educational Research, 11e

11-‹#›

Types of Single-Subject Designs

Multiple-baseline design

Behavior 1 O O OXOXOXOXOXOXOXOXOXO

Behavior 2 O O O O OXOXOXOXOXOXOXO

Behavior 3 O O O O O O OXOXOXOXOXO

Multiple-baseline designs can be combined with A-B-A designs when one can return to baseline.

Gay & Mills

Educational Research, 11e

11-‹#›

Types of Single-Subject Designs

Alternating treatments design: Includes the relatively rapid alternation of treatments for a single subject. Treatments are symbolized as T with subscripts (T1, T2). Treatments are randomly applied.

Strengths:

No withdrawal is necessary for alternating treatments designs

No baseline phase is necessary because the goal is to compare treatments against each other.

A number of treatments can be studied quickly and efficiently

A weakness, however, is carryover effects.

Gay & Mills

Educational Research, 11e

11-‹#›

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.

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

Gay & Mills

Educational Research, 11e

11-‹#›

Threats to Validity

Single-subject designs suffer from low external validity.

The effect of the baseline phase may pose an external validity threat in single-subject designs.

Similar to the pretest-treatment interaction threat in group designs.

Gay & Mills

Educational Research, 11e

11-‹#›

Threats to Validity

Single-subject studies, if executed properly, can have sound 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.

Gay & Mills

Educational Research, 11e

11-‹#›

Threats to Validity

Internal validity

Instrumentation is a threat to internal validity in single-subject designs.

Observations should be standardized

Instruments must be reliable and valid

Intra-observer reliability and inter-observer reliability are critical for effective single-subject studies.

Treatment should be explained in enough detail to permit replication.

Gay & Mills

Educational Research, 11e

11-‹#›

Threats to Validity

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

Gay & Mills

Educational Research, 11e

11-‹#›

Replication

External validity in single-subject designs is established through replication.

Direct: Replication by the same investigator in a specific setting with the same or different participants.

Simultaneous: Replication with a number of participants with the same problem at the same location and same time can promote generalizability.

Systematic: Follows direct replication with different investigators, behaviors, and settings.

Clinical: Involves the development of a treatment package of two or more interventions found to be individually successful.

Gay & Mills

Educational Research, 11e

11-‹#›