Implementation fidelity in a complex intervention promoting psychosocial well-being following stroke: an explanatory sequential mixed methods study

BACKGROUND: Evaluation of complex interventions should include a process evaluation to give evaluators, researchers, and policy makers greater confidence in the outcomes reported from RCTs. Implementation fidelity can be part of a process evaluation and refers to the degree to which an intervention is delivered according to protocol. The aim of this implementation fidelity study was to evaluate to what extent a dialogue-based psychosocial intervention was delivered according to protocol. A modified conceptual framework for implementation fidelity was used to guide the analysis. METHODS: This study has an explanatory, sequential two-phase mixed methods design. Quantitative process data were collected longitudinally along with data collection in the RCT. Qualitative process data were collected after the last data collection point of the RCT. Descriptive statistical analyses were conducted to describe the sample, the intervention trajectories, and the adherence measures. A scoring system to clarify quantitative measurement of the levels of implementation was constructed. The qualitative data sources were analyzed separately with a theory-driven content analysis using categories of adherence and potential moderating factors identified in the conceptual framework of implementation fidelity. The quantitative adherence results were extended with the results from the qualitative analysis to assess which potential moderators may have influenced implementation fidelity and in what way. RESULTS: The results show that the core components of the intervention were delivered although the intervention trajectories were individualized. Based on the composite score of adherence, results show that 80.1% of the interventions in the RCT were implemented with high fidelity. Although it is challenging to assess the importance of each of the moderating factors in relation to the other factors and to their influence on the adherence measures, participant responsiveness, comprehensiveness of policy description, context, and recruitment appeared to be the most prominent moderating factors of implementation fidelity in this study. CONCLUSIONS: This evaluation of implementation fidelity and the discussion of what constitutes high fidelity implementation of this intervention are crucial in understanding the factors influencing the trial outcome. The study also highlights important methodological considerations for researchers planning process evaluations and studies of implementation fidelity. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02338869; registered 10/04/2014. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12874-019-0694-z) contains supplementary material, which is available to authorized users.