Evaluating implementation fidelity in the PACE-UP (Pedometer and Consultation Evaluation-UP) complex walking intervention

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The problem

Implementation fidelity evaluation is crucial in complex interventions, as highlighted by recent MRC guidance, yet is often not reported. The PACE-UP trial used a pedometer and physical activity (PA) diary by post or combined with 3 practice nurse consultations to increase walking in 45-74 year olds from 7 SW London practices. We used the modified Conceptual Framework for Implementation Fidelity, assessing adherence (coverage, frequency, duration, content) and moderating factors (quality of delivery, participant responsiveness).

The approach

We assessed recruitment (coverage). For the nurse group we assessed: frequency (sessions attended); duration (session length, by self-report and audio-recording); content (nurse checklists); quality; and participant responsiveness for different trial aspects. For both groups we assessed the number returning completed PA diaries (participant responsiveness).


Trial recruitment was 9% (1033/11015). 74% (258/351) of nurse group participants attended all 3 consultations. Planned consultation durations were 30 minutes (session 1) and 20 minutes (sessions 2 and 3). Mean durations for session 1 were 30 (range 20-60) minutes for self-report, 26 (12-57) minutes for audio-recorded; and for sessions 2 and 3, 23 (5-60) minutes for self-report, 17 (9-29) minutes for audio-recorded. Content adherence was high, mean completion at session 1 of 11/11 items and sessions 2 and 3 of 5/6 items. Quality of delivery: 89% (232/262) felt heard, understood and respected by the nurse. Participant responsiveness: 79% (208/262) reported the consultation number was just right; 76% (198/262) felt able to maintain PA changes; and across both groups 79 % (549/692) returned completed PA diaries.


Coverage was low, however other adherence aspects, quality of delivery and participant responsiveness demonstrate high implementation fidelity, suggesting strong internal validity for PACE-UP trial outcomes. We have demonstrated a useful model for evaluating implementation fidelity and we will discuss this in light of new MRC guidance on process evaluation in complex intervention trials.


  • Howard Emma, Queen Mary's University of London, London, UK
  • Furness Cheryl, Queen Mary's University of London, London, UK
  • Harris Tess, Queen Mary's University of London, London, UK
  • Kerry Sally, Brunel, University of London, London, UK
  • Victor Christina
  • Ussher Michael, Queen Mary's University of London, London, UK
  • Cook Derek, Queen Mary's University of London, London, UK