Addressing fidelity within complex health behaviour change interventions: a scoping review of fidelity frameworks and models

Fidelity is an important but under-addressed aspect of health behaviour change intervention research. Consensus is lacking regarding terminology, definitions, and conceptualisations. Fidelity frameworks and models can help people address fidelity in a structured way and ensure clarity and consistency of terminology, but they are underutilised to date. We aimed to identify and describe existing fidelity frameworks/models and compare these in terms of fidelity constructs included. We conducted a scoping review using a pre-specified search, dual independent screening, and data extraction. We analysed data using basic descriptive statistics and qualitative content analysis. We identified 20 fidelity frameworks/models. All frameworks/models included constructs relating to intervention delivery. All frameworks/models also included additional constructs; however, there was a lack of consensus across these, and whether they are components or moderators of fidelity. For health behaviour change researchers wishing to address fidelity, selecting a comprehensive framework/model that facilitates consideration of multiple constructs and that aligns with their intended purpose and context may be beneficial. Fidelity is a multi-faceted concept of which delivery is an important, but not the only, construct. Findings will help researchers consider fidelity in greater depth, apply and refine existing frameworks/models, and improve how fidelity is addressed in future behavioural interventions.