Single-Case Experimental Design

Single-case experimental design (SCED) is a family of rigorous within-subject experimental methodologies for evaluating whether an intervention causes change in an individual, widely used in rehabilitation, special education, and applied behavior analysis. Rather than averaging across a large sample, SCED measures a defined target behavior repeatedly across a baseline (A) phase and an intervention (B) phase, and infers a causal effect when the change is replicated at three or more different points in time within the same case. Internal validity is built into the design itself through systematic manipulation of the independent variable and repeated demonstrations of effect, not through a control group. The 2013 What Works Clearinghouse single-case design standards, formalized by Kratochwill and colleagues, codified what counts as a credible SCED, including requirements for systematic manipulation, at least three attempts to demonstrate an effect, and minimum data points per phase. SCED is the experimental backbone of evidence-based practice for individuals whose conditions, contexts, or low incidence make group designs impractical.