Glossary
Intervention fidelity
What is intervention fidelity?
Intervention fidelity is the extent to which an intervention is delivered as intended. It concerns what was actually delivered, how much, and how consistently it matched the planned approach.
Measuring intervention fidelity
Carroll and colleagues organize adherence around content, frequency, duration, and coverage: what was delivered, how often, for how long, and to whom. They treat delivery quality and participant responsiveness as possible influences on that adherence. These are related questions, not interchangeable measures.
How fidelity helps interpret outcomes
Fidelity information helps interpret an evaluation alongside outcomes, participation, and context. Finding that parts of a program were omitted does not prove that the full program would have worked. Implementation problems and flaws in the intervention’s underlying theory can coexist.
Example of low intervention fidelity
If a course omits several planned exercises, evaluators should record the omission and examine its implications. They should not automatically conclude that an unchanged outcome was caused by the omission.
The implementation-fidelity framework
Carroll and colleagues’ implementation-fidelity framework provides the conceptual basis. The authors describe it as a framework needing empirical testing, rather than a rule that identifies the cause of every unsuccessful intervention.