Criteria for evaluating transferability of health interventions: a systematic review and thematic synthesis

Background: Improving the public's health in different countries requires the consideration of diverse health care systems and settings. For evidence-based public health, decision-makers need to consider the transferability of effective health interventions from a primary context to their specific target context. The aim of this systematic review was to develop a model for the assessment of transferability of health interventions through identification and systematization of influencing criteria, including facilitators and barriers. Methods: A systematic literature search was performed in the databases PubMed, Embase, CINAHL, and PsycINFO. Articles were eligible if they were published in English or German and provided a description of transferability criteria. Included articles were ranked based on their thematic relevance and methodological support of transferability criteria. Using a qualitative approach, a thematic synthesis was conducted. Results: Thirty-seven articles were included in the review. The thematic synthesis revealed 44 criteria, covered by 4 overarching themes, which influence transferability of health interventions: The population (P), the intervention (I), and the environment (E) represent 30 conditional transferability criteria, and the transfer of the intervention (T) represents 14 process criteria for transferring the intervention to the target context. Transferability (-T) depends on the dynamic interaction of conditional criteria in the primary and target context as well as on the process of transfer. The description of facilitators and barriers deepens the understanding of the criteria. The synthesis resulted in two related models: the conceptual PIET-T model explains the underlying mechanism of transferability of health interventions and the PIET-T process model provides practical guidance for a transferability assessment. Conclusions: Transferability of health interventions is a complex concept, which needs systematic consideration of the primary and target context. It should be anticipated before and evaluated after an intervention is implemented in the target context. Therefore, decision-makers need systematic and practically relevant knowledge on transferability. The synthesized PIET-T conceptual and process models with systematized criteria, facilitators, and barriers are intended as a theoretical basis to determine transferability of health interventions. Further research is needed to develop a practical tool for the PIET-T models and to evaluate the tool's usefulness for decision-making processes and intervention transfer.