1. Single-Subject Experimental Research
Educational Research
Chapter 10
Single-Subject Experimental Research
Gay, Mills, and Airasian

2. Single-Subject Research
Topics discussed in this chapter
The unique characteristics of single-subject designs
External and internal validity
Designing single-subject research
Three types of single subject designs
Analyzing data
Replication

3. Single-Subject Research
Two unique characteristics
The sample size is one subject
Each subject serves as his or her own control
Notation
‘A’ indicates a non-treatment phase usually referred to as a “baseline”
‘B’ indicates a treatment phase
Examples
A-B-A indicates a non-treatment baseline phase followed by a treatment phase which is followed by a return to a non-treatment baseline phase
A-B-A-B indicates four phases of treatment (baseline, treatment, baseline, and treatment)
Objectives 1.1, 1.2, 1.5

4. Single-Subject Research
Why use a single-subject design?
In some situations it is unethical to deny a control group treatment, so a single-subject design is the alternative
Denying Title I resources to children who qualify for them
In other situations there are low incidences of subjects available to participate
Children with specific special needs
Objective 1.3

5. Single-Subject Research
External validity
The lack of external validity is the major concern with single-subject designs
Generalizability is addressed through multiple replications of the same treatment and design that produce similar results for a number of different participants
Objective 1.4

6. Single-Subject Research
Internal validity
Internal validity is always a concern with single-subject research
Two major threats
Instrumentation
Specificity of variables
Controlling threats
Baselines are multiple measures of pretest performance
By repeating baseline measures over a period of time threats to internal validity can be controlled
History
Maturation
Objectives 1.6 & 1.7

7. Single-Subject Research
Number of manipulated variables
Only a single variable should be manipulated in single-subject designs
Adding and withdrawing more than one variable becomes problematic in terms of analyzing the individual effect of either variable
Objective 1.8

8. Single-Subject Designs
Three major categories
A-B-A withdraw
Alternating phases of baseline (A) and treatment (B)
Alternatives include the A-B-A-B design
Multiple baselines
The systematic addition of behaviors, subjects, or settings for intervention
Used when baselines cannot be recovered after treatment has been received
Objective 1.9

9. Single-Subject Designs
Three major categories (cont.)
Alternating treatments
Rapid alternation of treatments to a single subject to assess the effectiveness of two or more treatments
Objective 1.9

10. A-B Withdraw Design The A-B design O O O O O O O X O X O X O X O
Baseline Treatment
Internal validity threats are of concern
Use of designs with additional baseline and/or treatment phases helps to control threats to internal validity
Objective 1.10

11. A-B-A Withdraw Design The A-B-A design O O O O X O X O X O O O O O
Baseline Treatment Baseline
If the outcome is better during treatment than either baseline, the treatment is likely effective
Internal validity threats can be controlled
The major concern
The experiment ends with the subject not receiving the treatment
If the treatment has been shown to be effective this is an ethical concern
Objective 1.10

12. A-B-A-B Withdraw Design
The A-B-A-B design
O O O O X O X O X O O O O O X O X O X O
Baseline Treatment Baseline Treatment
Internal validity threats can be controlled
The effects of the treatment can be demonstrated twice
If the results are the same, it is likely the influence of extraneous variables has been controlled
Ethical concerns related to the A-B-A design are eliminated
The right pattern of results provides convincing evidence of the effectiveness of the treatment
Objective 1.10

13. Multiple Baseline Designs
Three basic multiple baseline designs
Across behaviors
Data are collected on several behaviors for a single subject
Treatment is applied to each behavior one at a time until all behaviors have been treated
Across subjects
Data are collected on several subjects for one behavior
Treatment is applied to each subject one at a time until all subjects have been treated
Objective 2.1

14. Multiple Baseline Designs
Three basic multiple baseline designs (cont.)
Across settings
Data are collected on one behavior for one subject across several settings
Treatment is applied to each behavior one at a time in each setting until all settings have been treated
Objective 2.1

15. Multiple Baseline Designs
Three basic multiple baseline designs (cont.)
An example across behaviors
Behavior 1 O O X O X O X O X O X O
Behavior 2 O O O O X O X O X O X O
Behavior 3 O O O O O O X O X O X O
Design concerns
If behaviors are treated the behaviors must be independent of one another
If subjects are treated the subjects must be similar
If settings are treated the settings must be as natural as possible
Objective 2.1

16. Multiple Baseline Designs
Advantages
Can be used when baseline data are not recoverable after treatment
The effects of reinforcement are designed to be maintained after the reinforcement is removed
Can be combined with A-B-A designs to establish a very convincing case for cause and effect
An A-B-A design is applied across three behaviors
Objective 2.2

17. Alternating Treatments Design
Involves the relatively rapid alternation of treatments for a single subject
Treatment does not occur at fixed time periods
Treatments are changed sporadically
Advantages
Useful in assessing the relative effectiveness of two or more treatments
No withdraw of treatment is necessary
No baseline is needed
The effects of treatment can be studied quickly and efficiently
Objectives 3.1 & 3.2

18. Data Analysis and Interpretation
Two phases
An evaluation of the adequacy of the design
An assessment of the treatment effectiveness
Two techniques
Visual inspection of the data
Graphical presentation of the results
Objective 4.1

19. Data Analysis and Interpretation
Significance
Clinical significance
Effects related to the behaviors being treated
Meaningful in a “real” sense
Parallels the importance of practical significance
Statistical significance
Statistical tests are available but often result in statistical significance that has little if any clinical significance
Use is currently debated in the field
Objective 4.2

20. Replication
Replication is an important aspect of single-subject research
The more one’s results are replicated the more confidence one has in the procedures that produced the results
Three stages of replication
Direct replication
Same researcher, same subjects, specific setting
Simultaneous replication refers to the use of different subjects and increases the generalizability of the study
Objectives 5.1 & 5.2

21. Replication Three stages of replication (cont.) Systematic replication
Follows direct replication efforts
Involves different researchers, behaviors, or settings
Over time techniques are identified that consistently produce effective results
Clinical replication
Follows systematic replication
Involves the development of treatment packages composed of two or more effective treatments
Objective 5.2