Fidelity of intervention delivery in psychosocial and behavioral programs (FIPP): A modified Delphi study and final guideline

Introduction: Fidelity-ensuring interventions are implemented as intended-is a key focus in implementation science. Despite its benefits in research and practice, data on the fidelity of implementation are often overlooked, measured inconsistently, or underreported. In 2024, we proposed a preliminary guideline for one component of fidelity-the fidelity of delivery in parenting interventions. This study builds upon that work, refining the guideline for psychosocial and behavioral interventions. Methods: Using a modified Delphi technique, we refined the Fidelity of Intervention delivery in Psychosocial and behavioral Programs (FIPP) guideline. The process included survey responses (n = 34), two panel consensus meetings (n = 10), and email feedback (n = 5) resulting in six rounds of iterative revisions to produce the final FIPP. Results: The modified Delphi technique resulted in a final FIPP with 35 items across six categories: intervention, facilitator, fidelity measure, and fidelity assessor characteristics; fidelity assessment method; and fidelity results and discussion. The final FIPP was produced based on engagement and data from the survey participants, consensus meeting panelists, and email panelists. Conclusions: This study advances reporting on fidelity of delivery in psychosocial and behavioral interventions by refining the FIPP guideline through a rigorous, consensus-driven process. The FIPP provides a comprehensive structure to improve the consistency and transparency of fidelity of delivery assessment. By promoting standardized reporting, the FIPP enhances the quality of implementation science, ultimately supporting more effective interventions and better participant outcomes. Researchers and practitioners are encouraged to adopt the FIPP to strengthen intervention fidelity and drive meaningful progress in the field.