Identifying the PECO: A framework for formulating good questions to explore the association of environmental and other exposures with health outcomes.

[First paragraph] A clearly-framed question creates the structure and delineates the approach to defining research objectives, conducting systematic reviews and developing health guidance (Guyatt et al., 2011; Armstrong et al., 2007). To assess the association between exposures and outcomes, including in the field of nutrition, environmental and occupational health, the concept of defining the Population (including animal species), Exposure, Comparator, and Outcomes (PECO) as pillars of the question is increasingly accepted (Morgan et al., 2016; Morgan et al., n.d.). Thus, the PECO defines the objectives of the review or guideline. Furthermore, the PECO informs the study design or inclusion and exclusion criteria for a review, as well as facilitating the interpretation of the directness of the findings based on how well the actual research findings represent the original question.