Evidence Synthesis and Integration in the IRIS Program-Abstract
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Systematic reviews conducted as part of developing Integrated Risk Information System (IRIS) assessments consist of structured processes for identifying, evaluating, and summarizing relevant evidence (i.e., evidence synthesis), and arriving at summary conclusions regarding the overall body of evidence (i.e., evidence integration). These approaches were developed through discussions within EPA and informed by multiple reviews by the National Research Council (2011; 2014; 2018). In addition, IRIS assessments include quantitative toxicity values based on the evidence identified as most informative during the systematic reviews. The standard operating procedures, including frameworks and considerations for developing the different parts of the systematic reviews, are outlined in an internal document. For each potential human health hazard, the evidence synthesis builds from the outcome-specific evaluations of individual studies and discusses additional considerations across the sets of pertinent studies to summarize the available evidence in a manner that informs an evaluation of the body of evidence during evidence integration. A primary goal of the evidence synthesis is to evaluate potential sources of heterogeneity across the study results, which informs evaluations of each Hill criterion. Evidence integration is a two-step process based on structured, example-based frameworks for applying an adapted set of considerations described by Sir Bradford Hill (1965), first to each line of evidence, and then across all evidence. Evidence integration is also applied to directly inform study selection and toxicity value derivation.