2015 Dietary Guidelines Advisory Committee (DGAC) Nutrition Evidence Library Methodology
Describe and Synthesize the Evidence
Evidence Synthesis, Conclusion Statements, Grading Evidence, & Research Recommendations
Evidence synthesis is the process by which the DGAC compared, contrasted, and combined evidence from multiple studies to develop key findings and a graded conclusion statement that answered the SR question. This qualitative synthesis of the body of evidence involved identifying overarching themes or key concepts from the findings, identifying and explaining similarities and differences between studies, and determining whether certain factors affected the relationships being examined. To facilitate the DGAC’s review and analysis of the evidence, staff prepared a “Key Trends” template for each SR question. This document was customized for each question and included questions related to major trends, key observations, themes for conclusion statements and key findings. It also addressed methodological problems or limitations, magnitude of effect, generalizability of results, and research recommendations. DGAC members used the description of the evidence, along with the full data extraction grid, and full-text manuscripts to complete the “Key Trends” questions. The responses were compiled and used to draft the qualitative evidence synthesis and the conclusion statement.
The conclusion statement is a brief summary statement worded as an answer to the SR question. It must be tightly associated with the evidence, focused on general agreement among the studies around the independent variable(s) and outcome(s), and may acknowledge areas of disagreement or limitations, where they exist. The conclusion statement reflects the evidence reviewed and does not include information that is not addressed in the studies. The conclusion statement also may identify a relevant population, when appropriate. In addition, “key findings” (approximately 3 to 5 bulleted points) were drafted for some questions to provide context and highlight important findings that contributed to conclusion statement development (e.g., brief description of the evidence reviewed, major themes, limitations of the research reviewed or results from intermediate biomarkers).
Develop Conclusion Statements, Evidence Grade, and Research Recommendations
The DGAC used predefined criteria to evaluate and grade the strength of available evidence supporting each conclusion statement. The grade communicates to decision makers and stakeholders the strength of the evidence supporting a specific conclusion statement. The grade for the body of evidence and conclusion statement was based on five elements outlined in the NEL grading rubric: quality, quantity, consistency, impact, and generalizability.
Based on the existing body of evidence, research gaps, and limitations, the DGAC formulated several research recommendations that could advance knowledge related to the SR question. These recommendations can be used to inform research agendas and further inform policymakers.
Related 2015 DGAC Methodology topics:
Last Updated: 12/16/2014