Compare methods

	Single-System Design	ABAB design
Field	Social Work	Experimental design
Family	Process / pipeline	Process / pipeline
Year of origin	2009	1960s (Sidman 1960; Baer et al. 1968)
Originator	Martin Bloom, Joel Fischer & John G. Orme (codification in social work)	Murray Sidman; Baer, Wolf & Risley (applied behavior analysis formalization)
Type	Time-series design for evaluating intervention with a single client system	Single-subject experimental design
Seminal source	Bloom, M., Fischer, J., & Orme, J. G. (2009). Evaluating Practice: Guidelines for the Accountable Professional (6th ed.). Pearson/Allyn & Bacon. ISBN: 9780205458066	Sidman, M. (1960). Tactics of Scientific Research: Evaluating Experimental Data in Psychology. Basic Books.
Aliases	Single-Subject Design, Single-Case Design, N-of-1 Design, Single-System Evaluation	reversal design, withdrawal design, ABAB reversal, operant reversal design
Related	4	6
Summary	A single-system design is a time-series approach to evaluating practice in which a single client system — an individual, family, group, or organization — is measured repeatedly on a clearly defined target before and during (and sometimes after) an intervention. By tracking the same system over time rather than comparing a treatment group to a control group, it lets a practitioner judge whether their own intervention is associated with change in the people they actually serve. It is the methodological backbone of the 'accountable professional' tradition codified by Bloom, Fischer, and Orme.	The ABAB design is a single-subject experimental methodology that establishes causal control by repeatedly introducing and removing an intervention. A baseline phase (A) is followed by an intervention phase (B), then a return to baseline (A), and a second intervention phase (B), allowing the researcher to demonstrate that observed behavior changes are produced by the intervention rather than by coincidental factors.