A six-step protocol to systematic process evaluation of multicomponent cluster-randomised health promoting interventions illustrated by the Boost study

• We present a systematic protocol to planning process evaluation.
• The protocol was applicable in a multicomponent intervention.
• The protocol ensures assessment of important aspects of the implementation process.
• The protocol can help identify barriers and facilitators for implementation.
• Data from the protocol provide insight into working mechanisms of the intervention.

BackgroundIn multicomponent interventions it is important to examine the implementation of each component to enable valid assessments of the effectiveness of each component. Many studies do not systematically document, evaluate and report the level of implementation and there is a lack of systematic approaches to conduct process evaluation studies to guide researchers and evaluators.The aim of this study was to present a systematic approach to plan process evaluation of the implementation of randomised multicomponent interventions.MethodsBuilding on existing process evaluation frameworks and concepts, we developed a six-step protocol: 1. Brainstorm of processes necessary for full implementation and potential barriers and facilitators to implementation; 2. Application of process evaluation concepts to ensure inclusion of important implementation processes; 3. Measurement of proximal outcomes; 4. Identification of relevant data sources; 5. Selection of methods and timing of data collection of process measures; 6. Development of instruments. The protocol was applied to the Boost study, a multicomponent school-based dietary intervention.Results and conclusionsThe protocol was readily applicable for planning process evaluation of environmental and educational intervention components in a school setting. The protocol ensures systematic assessment of the implementation processes that are crucial for interpretation of intervention effects.Trial registrationCurrent Controlled Trials ISRCTN11666034.