Assessing intervention fidelity in a nationally implemented diabetes prevention programme delivered by multiple providers

Student thesis: Phd


Intervention fidelity is defined as the extent to which an intervention is implemented as intended. Without an assessment of fidelity, it cannot be ascertained why interventions are effective or ineffective, and reasons for this. A leading framework for examining fidelity was proposed by the National Institutes of Health Behaviour Change Consortium, stipulating assessment of five domains: design (whether intervention plans are in accordance with the evidence base), training (of staff to deliver intervention components), delivery (of intervention components), receipt (participant understanding of intervention content), and enactment (participant use of intervention content in their day-to-day lives). This thesis presents a programme of research assessing fidelity of the National Health Service Diabetes Prevention Programme (NHS-DPP); a behaviour change intervention for adults in England who are at an increased risk of developing type 2 diabetes. The programme was launched in 2016 and delivered by four independent provider organisations. There are few examples of examining fidelity of large-scale nationally implemented programmes. Assessing fidelity of large-scale programmes is important due to the multiple stakeholders (e.g., commissioners, independent providers) involved at each stage of programme implementation, and the higher risk of dilution of fidelity from the set guidelines through to receipt of the programme. This thesis presents eight published research articles evaluating fidelity of the NHS-DPP as evidence of my significant contribution to the literature for the assessment of fidelity in large-scale behaviour change programmes. An evaluation of underpinning theory of the NHS-DPP is presented in publication 1 and fidelity of design is evaluated in publication 2. Fidelity of staff training is assessed in publication 3. Three papers assessing fidelity of delivery of the programme are described in publications 4-6. Publication 7 describes an interview study assessing service user receipt and enactment of the NHS-DPP intervention content. Finally, publication 8 reflects on the lessons learned for implementing large-scale behaviour change programmes delivered by multiple providers. This thesis (a) describes the methods used to assess fidelity for large-scale programmes delivered by multiple providers, which have since been used for fidelity evaluations of other nationally implemented NHS services, (b) identifies how the behaviour change content in the NHS-DPP can be improved during the intervention design, staff training and delivery for future roll-outs of the programme, and (c) has informed working with NHS England to improve the behaviour change content in the NHS-DPP. This work makes a substantial contribution to assessing fidelity of the behaviour change content in large-scale interventions delivered by multiple providers.
Date of Award1 Aug 2024
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorDavid French (Supervisor)


  • Implementation science
  • Programme implementation
  • Behaviour change
  • Intervention fidelity
  • Diabetes prevention

Cite this