Single-subject experimental design for evidence-based practice

Abstract

Purpose: Single-subject experimental designs (SSEDs) represent an important tool in the development and implementation of evidence-based practice in communication sciences and disorders. The purpose of this article is to review the strategies and tactics of SSEDs and their application in speech-language pathology research.

Method: The authors discuss the requirements of each design, followed by advantages and disadvantages. The logic and methods for evaluating effects in SSED are reviewed as well as contemporary issues regarding data analysis with SSED data sets. Examples of challenges in executing SSEDs are included. Specific exemplars of how SSEDs have been used in speech-language pathology research are provided throughout.

Conclusion: SSED studies provide a flexible alternative to traditional group designs in the development and identification of evidence-based practice in the field of communication sciences and disorders.

Figures

FIGURE 1

Hypothetical data demonstrating unambiguous changes in level (Panel A), trend (Panel B), and variability (Panel C).

FIGURE 2

Hypothetical data demonstrating demonstrations of non-effect: delayed latency to change (Panel A), trend in desired direction during baseline phase (Panel B), highly variable data with overlap between baseline and intervention phases (Panel C).

FIGURE 3

Percentage of trials containing vocal approximations during no positive reinforcement of vocalization (baseline; see Panel A) and positive reinforcement of vocalization (see Panel B), using an ABAB design. Voc. = vocal; PR = positive reinforcement. From “The Picture Exchange Communication System: Effects on manding and speech development for school-aged children with autism,” by Tincani, Crozier, and Alazetta, 2006, Education and Training in Developmental Disabilities, 41, p. 183. Copyright 2006 by Council for Exceptional Children, Division on Developmental Disabilities. Reprinted with permission.

FIGURE 4

Percentage of unprompted questions asked by three participants in baseline, intervention, and generalization sessions using a multiple-baseline, across-participants design. From “Question-asking and collateral language acquisition in children with autism,” by Koegel, Koegel, Green-Hopkins, and Barnes (2010), Journal of Autism and Developmental Disorders, 40, p. 512. Copyright 2009 by the authors. Reprinted with permission.

FIGURE 5

Speech volume during a token reinforcement intervention and follow-up using a changing-criterion design. From “A controlled single-case treatment of severe long-term selective mutism in a child with mental retardation,” by Facon, Sahiri, and Riviere, (2008), Behavior Therapy, 39, p. 313. Copyright 2008 by Elsevier. Reprinted with permission.

FIGURE 6

Percent of intervals with challenging behavior and mands during functional analysis, intervention demonstration, and component analysis. From “A component analysis of functional communication training across three topographies of severe behavior problems,” by Wacker et al., 1990, Journal of Applied Behavior Analysis, 23, p. 424. Copyright 2008 by the Society for the Experimental Analysis of Behavior. Reprinted with permission.

FIGURE 7

Number of correct responses and tongue clicks during discrete trial training sessions in Spanish (Sp.) and English (Eng.) using an alternating treatments design. From “Effects of language instruction on response accuracy and challenging behavior in a child with autism,” by Lang et al., 2011, Journal of Behavioral Education, 20, p. 256. Copyright 2001 by Springer Science+Business Media, LLC. Reprinted with permission.

FIGURE 8

Number of phrases signed correctly during directed rehearsal, directed rehearsal with positive reinforcement, and control sessions using an adapted alternating treatments design. From “Acquisition and generalization of manual signs by hearing-impaired adults with mental retardation,” by Conaghan, Singh, Moe, Landrum, and Ellis, 1992, Journal of Behavioral Education, 2, p. 192. Copyright 1992 by Human Sciences Press. Reprinted with permission.