Protocol for the process evaluation of a mobile produce market intervention to increase fruit and vegetable consumption in lower-income communities: the Veggie Van Study

Introduction: Mobile produce markets have become increasingly prevalent throughout the United States, highlighting the need for evidence-based models for markets to follow. The Veggie Van (VV) model is a set of practices that have been found to be efficacious in increasing fruit and vegetable intake in underserved communities. The next step in determining the model's effectiveness is evaluating the model when implemented on a broader scale under real-world conditions. As part of a multi-state randomized controlled effectiveness trial, the Veggie Van Study, an extensive process evaluation of the implementation of the VV model was conducted. Methods: Nine partner organizations agreed to implement the VV model at newly launched mobile markets over a 12-month period. Organizations received funding, training, and technical assistance to support implementation of the model. In addition to facilitating participant recruitment and data collection, partners agreed to participate in implementation-related data collection. Data collection methods include quantitative process measures surveys, qualitative interviews, and mobile market sales data. The main process outcomes are fidelity, dose delivered, penetration, maintenance of the VV model, and contextual factors related to implementation. Discussion: This extensive mixed-methods process evaluation addresses a gap in the literature for transparent reporting of process evaluations; it also provides a model for similar community-based interventions to follow. Understanding the implementation process and the context surrounding implementation of the VV model is critical for interpreting effectiveness findings (i.e., dietary changes) and optimizing the intervention. Clinical trial registration: https://clinicaltrials.gov/study/NCT04246593, NCT04246593.