Single-Case Experimental Design
Also known as: Single-Subject Experimental Design, N-of-1 Experimental Design, Single-Case Research Design, SCED
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.
Key highlights
- Establishes experimental control and causal inference for a single individual without requiring a control group or large sample.
- Ideal for low-incidence, heterogeneous, or clinical populations where group randomized trials are infeasible.
- Repeated within-person measurement reveals trajectory, immediacy, and variability of response that group means obscure.
- Backed by formal design standards that make studies appraisable, comparable, and aggregable into evidence reviews.
Intuition
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How it works
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When to use it
Use single-case experimental design when you need rigorous causal evidence about whether an intervention works for a specific individual or a small set of individuals, and when a group design is impractical or inappropriate. It is the method of choice for low-incidence conditions, heterogeneous populations, and clinical or educational settings where each person's response matters and large samples cannot be assembled — common throughout rehabilitation, special education, and behavior analysis. SCED requires a target behavior that can be measured repeatedly and a context in which the intervention can be systematically introduced, withdrawn, or staggered to create replicated demonstrations of effect. It is less suitable when the outcome cannot be measured frequently, when withdrawal of an effective treatment would be unethical and no staggered alternative exists, or when the research question is genuinely about average effects across a population, where a group design is preferable.
Strengths & limitations
- Establishes experimental control and causal inference for a single individual without requiring a control group or large sample.
- Ideal for low-incidence, heterogeneous, or clinical populations where group randomized trials are infeasible.
- Repeated within-person measurement reveals trajectory, immediacy, and variability of response that group means obscure.
- Backed by formal design standards that make studies appraisable, comparable, and aggregable into evidence reviews.
- External validity is limited; demonstrating an effect in one or a few cases does not establish generalization without systematic replication.
- Requires behaviors that can be measured repeatedly and reliably, which excludes outcomes that change slowly or cannot be sampled often.
- Designs relying on withdrawal of treatment can be ethically problematic or impossible for irreversible learning.
- Strong serial dependence in within-person time series complicates statistical analysis and visual interpretation.
Common pitfalls
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Applications
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Frequently asked
How is a single-case experimental design different from a simple before-and-after comparison?
A before-and-after comparison measures the outcome once before and once after an intervention and is correlational: any change could be due to maturation, history, or chance. A single-case experimental design measures the behavior repeatedly to establish a stable baseline, has the experimenter systematically manipulate the intervention, and replicates the effect at three or more points in time. That replication within the same case is what rules out rival explanations and licenses a causal claim, which a one-shot pre-post comparison cannot support.
Why does the design require three demonstrations of an effect?
A single change in behavior when an intervention starts might coincide with some other event, so one demonstration is not convincing. Each additional successful demonstration — through reversal, staggered introduction across baselines, or alternation — creates another moment where the behavior changes only when the intervention is present, and each one multiplies the implausibility of a coincidental explanation. Kratochwill and colleagues set three as the threshold in the 2013 design standards because three independent demonstrations provide a credible experimental basis for inferring control within a single case.
Can single-case experimental designs contribute to evidence-based practice?
Yes. Because the 2013 design standards make individual studies appraisable and gradeable, well-conducted single-case studies can be rated for quality and aggregated across cases and studies to support claims of generalization. This is essential in fields like special education and rehabilitation where group randomized trials are often infeasible. Systematic replication across individuals, settings, and researchers, combined with effect-size summaries, allows single-case evidence to inform practice guidelines for populations that group designs struggle to reach.
Sources
- 1.Kratochwill, T. R., Hitchcock, J. H., Horner, R. H., Levin, J. R., Odom, S. L., Rindskopf, D. M., & Shadish, W. R. (2013). Single-case intervention research design standards. Remedial and Special Education, 34(1), 26-38.
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Cite this page
ScholarGate. (2026, June 23). Single-Case Experimental Design. ScholarGate. https://scholargate.app/disability-studies/single-case-experimental-design