Fidelity is the extent to which the planned behaviour change intervention scenario is realised in the actual behaviour change intervention scenario.

The Intervention Fidelity Ontology specifies fidelity enhancing processes, fidelity assessment processes, and fidelity data items for different types of fidelity of the intervention scenario (e.g. fidelity of intervention content, fidelity of setting). The Intervention Fidelity Ontology is currently under development.