Single-System Design

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.