Background: The processes at play in the implementation of one program in different contexts are complex and not yet well understood. In order to facilitate both the analysis and transfer of interventions, a "key functions/implementation/context" (FIC) model was developed to structure the description of public health interventions by distinguishing their potentially transferable dimensions (their "key functions") from those associated with their translation within a specific context (their "form"). It was used to describe and compare preschool preventative nutrition interventions routinely implemented across three territories, in accordance with same national specifications.
Methods: The interventions were independently described by researchers and intervention's implementers using the FIC model, during several workshops. Their key functions were then classified into 12 themes and compared to assess the extent to which the three interventions were similar.
Results: Despite being produced from the same set of specifications and having similar objectives, the key functions of the interventions in the three departments mostly reflected the same major themes, they did not overlap and were in some cases very different. In one of the three departments, the intervention was markedly different from those of the other two departments. The historical context of the interventions and the specificities of the local actors appear highly determinant of the key functions described.
Conclusions: For the interventions that we studied, some of the key functions varied greatly and translated different concepts of health education and modes of intervention to the population. It now seems vital to improve the description of interventions on the ground in order to highlight the key functions on which they are based, which still often remain implicit. The FIC model could be used to complement other models and theories focusing on the description of the implementation process, its determinants or its evaluation. Its interest is to provide a structure for joint reflection by various actors on the transferable aspects of an intervention, its form and its interactions with the context, in order ultimately to analyse or to improve its potential transferability.
Keywords: Context; Form; Interventions; Key function; Nutrition; Public health; School; Transferability.