Chapter 11: Single-Subject Experimental Research

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 research. • 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.

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.

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 her own control.

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 in special education, communication science disorders, and clinical psychology. • Applications of these designs, however, are appropriate to many additional areas of research.

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.

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.

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.

8. Single-Subject Experimental Designs • Single-subject designs suffer from low external validity. • Replication is the key to generalizability in single-subject designs. • 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.

9. 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.

10. 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 permit replication.

11. 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.

12. Types of Single-Subject Designs • A-B-A withdrawl 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

13. Types of Single-Subject Designs • Additive designs • 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.

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

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.

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.

17. Data Analysis and Interpretation • Although available, inferential statistical procedures are not often used in single-subject designs. • External validity in single-subject designs is established through replication.

18. Data Analysis and Interpretation • 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.

19. Data Analysis and Interpretation • Replication • Systematic: Follows direct replication with different investigators, behaviors, and settings. • Clinical replication involves the development of a treatment package composed of two or more interventions that have been found to be individually successful.