Making Sense of Single-Case Design Effect Sizes

Single-case research methods provide a basis for demonstrating that an intervention produces a reliable change in a targeted outcome for individual cases. To supplement visual analysis of data in single-case studies, researchers frequently report statistics—often referred to as effect sizes—to summarize study findings. The recent proliferation of effect sizes used in single-case research can be confusing. In this article, after reviewing single-case research, we provide an overview of common types of effect sizes used in single-case research, including overlap metrics and within- and between-participant effect sizes, and conclude with examples of these effect sizes in the single-case literature. Our take-home message is that effect sizes are useful complements to visual analysis when interpreting results of single-case design research studies.