Determining the Efficacy of Intervention: The Use of Effect Sizes for Data Analysis in Single-Subject Research

Abstract Use of the effect size as a descriptive statistic for single-subject research is presented. A brief review of visual and statistical analysis techniques commonly used in single-subject methods is provided, and the limitations of each are noted. Effect sizes are presented as statistics that can augment the interpretation of results as well as provide additional information about the effectiveness of interventions. Four types of treatment effects are presented, with corresponding case studies illustrating the computation and interpretation of the effect size for each. An appendix includes the case study data and a sample computer program for computing the effect sizes described.