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Related Experiment Video
Updated: May 27, 2025

A Within-Subject Experimental Design using an Object Location Task in Rats
Published on: May 6, 2021
Randomization in single-case design experiments: Addressing threats to internal validity.
Thomas R Kratochwill1, Joel R Levin2
1Department of Educational Psychology, University of Wisconsin-Madison.
Randomization enhances single-case experimental designs (SCEDs) by controlling validity threats often unaddressed by replication alone. This improves research credibility and statistical analysis for SCED intervention studies.
Area of Science:
- Psychology
- Research Methodology
- Behavioral Science
Background:
- Single-case experimental designs (SCEDs) are crucial for evaluating interventions.
- Traditional SCEDs rely heavily on replication to ensure internal validity.
- Threats to internal validity can persist even with replication in SCEDs.
Purpose of the Study:
- To review and detail various randomization strategies applicable to SCED methodology.
- To explicate how specific randomization techniques control threats to internal validity.
- To demonstrate the utility of randomization in both conventional and nonconventional SCEDs.
Main Methods:
- Review of existing literature on randomization in experimental designs.
- Categorization of randomization strategies: phase-order, between-intervention, within-intervention, and start-point randomization.
- Application of these strategies to various SCED variations (e.g., ABAB, alternating treatment, multiple baseline) and non-replication designs.
Main Results:
- Randomization offers explicit control over internal validity threats not fully addressed by replication.
- Specific randomization methods are detailed for diverse SCED structures.
- Randomization enhances scientific credibility, statistical conclusion validity, and likelihood of inclusion in literature syntheses.
Conclusions:
- Randomization is a vital tool for strengthening the internal validity of SCEDs.
- Implementing randomization increases the rigor and statistical power of SCED research.
- Recommendations are made for establishing randomization standards in SCED methodology.

