Outputs and moderating factors
Outputs are the activities undertaken when implementing a behaviour change intervention (8, 9). Historically, evaluation has focussed on the intervention’s effectiveness without evaluating fidelity (9). Fidelity is the degree to which an intervention is implemented as intended. It is essential for interpreting whether the observed outputs are a faithful measure of intervention effectiveness. Guidance for process evaluations of complex interventions emphasises the importance of evaluating fidelity, but does not provide recommendations regarding how to do it. Several frameworks are available to guide fidelity evaluation; however, they are frequently not adopted in trials of behaviour change interventions (9).
Evaluating fidelity has historically focussed on dose andreach, whereas fidelity of delivery, receipt and enactment are now recognised as important (9). The Conceptual Framework for Implementation Fidelity (8) measures four components of fidelity: content, coverage, frequency and duration of the intervention. It also captures four moderators of fidelity: intervention complexity, facilitation strategies, quality of intervention delivery and responsiveness of participants (8). By comprehensively capturing fidelity of each intervention component, it can also be determined which are essential to achieving the desired change in behaviour. Any adaptation or flexibility of intervention delivery should also be captured to understand how sites implement an intervention component(s) and how this variation impacts the intervention’s effectiveness.