Science-based decision-making in environmental health policy: What's systematic review got to do with it?

Synthesizing what is known about the environmental contributors of health is instrumental to taking action to prevent harm but methods of research synthesis commonly used in environmental health lag behind comprehensive, rigorous and transparent systematic review methods developed in the clinical sciences over the past 20 years. To address this gap, a systematic review methodology called the Navigation Guide was crafted and implemented by an interdisciplinary collaboration of scientists. The Navigation Guide proceeds from methods of research synthesis used in clinical settings but accounts for differences between environmental and clinical health sciences related to the evidence-base and decision-context. Objective:  Develop proof of concept of the Navigation Guide methodology. Method: Apply the methodology to 2 case studies: (1) prenatal exposure to perfluorooctanoic acid (PFOA) and fetal growth; and (2) prenatal exposure to triclosan and adverse reproductive and developmental health outcomes. Results: Clear, concise and transparently derived statements about the toxicity of PFOA and triclosan. Key points of departure from current methods of expert-based narrative review prevalent in environmental health include: an a priori protocol; standardized and transparent documentation including expert judgment; a comprehensive search strategy; assessment of “risk of bias”; and separation of the science from values and preferences. Key points of departure from evidence-based medicine include: human observational studies were assigned a “moderate” quality rating; and diverse evidence streams (human and non-human) were combined. Conclusion: The Navigation Guide methodology is a systematic and rigorous approach to research synthesis that has been developed to reduce bias and maximize transparency in the evaluation of environmental health information. While novel aspects of the method will require further development and validation, our findings demonstrated that improved methods of research synthesis under-development at the National Toxicology Program and under consideration by the U.S. Environmental Protection Agency are fully achievable.