Compare methods

	Single-System Design	AB Design
Field	Social Work	Experimental design
Family	Process / pipeline	Process / pipeline
Year of origin	2009	1960s
Originator	Martin Bloom, Joel Fischer & John G. Orme (codification in social work)	Murray Sidman; Baer, Wolf & Risley
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	baseline-intervention design, AB single-case design, AB phase 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 AB design is the simplest single-subject experimental design, consisting of two sequential phases: a baseline phase (A) in which the target behavior is observed under natural conditions without intervention, followed by an intervention phase (B) in which the treatment or manipulation is introduced. Changes in the behavior's level, trend, or variability between phases are used to infer the effect of the intervention on the individual participant.