An abductive inferential system approach to weight of evidence syntheses: the problem and military exposures worked example.

Objective: Weight of Evidence methods for evidence synthesis of etiological epidemiology questions regarding historical complex exposures have been developed in recent years but are still in their nascency. This manuscript describes a novel extension of existing methods to address situations where the exposure is historically bound, direct evidence is limited, and new research is unlikely. Principles are illustrated via a worked example in the military exposures context. Methods: Several existing methodological approaches were adapted and extended using an abductive reasoning approach. We demonstrate an approach to developing a logically interrelated system of PECO questions, integrating and evaluating multiple evidence streams to support inference to the best explanation. Results: A synthetic advancement on current WOE methods using an "inference to the best explanation" approach provides benefits over more traditional (deductive) methods of evidence synthesis. Concrete military exposure examples are provided. Conclusion: Applying this approach can provide a principled and transparent method of evidence synthesis to direct policy decisions under conditions of limited evidence and uncertainty.