Nutrition Evidence Systematic Review Methodology
NESR uses a rigorous and protocol-driven methodology to conduct systematic reviews.
Systematic reviews conducted by NESR answer important public health-related food and nutrition questions relevant to Federal policy and programs.
NESR’s work helps Federal agencies and programs uphold the Data Quality Act, which mandates that Federal agencies ensure the quality, objectivity, utility, and integrity of the information used to form Federal guidance.
Federal stakeholders are an important resource NESR uses to help identify high-priority systematic review questions. Questions are also informed by input from other stakeholders, such as scientific experts and the public. Learn more information about roles and responsibilities.
Our systematic review methodology, shown below, is designed to promote transparency, minimize bias, and ensure the availability of systematic reviews that are relevant, timely, and high quality.
Develop and Prioritize Questions
Federal stakeholders develop systematic review questions that:
- Address food and nutrition topics
- Are important to public health
- Can inform Federal guidance and programs
Systematic reviews take a lot of time and resources. Therefore, questions must be prioritized.
Develop an Analytic Framework
NESR analysts work with scientific experts to develop an analytic framework for the systematic review question that includes the:
- Population of interest
- Intervention/Exposure versus Comparator
This framework also defines key terms and identifies factors that could impact the relationship between the intervention/exposure and outcome.
Establish Inclusion and Exclusion Criteria
Systematic review questions are answered by examining evidence from all relevant studies. NESR analysts work with expert groups to establish a set of inclusion and exclusion criteria to specify what makes a study relevant for a given question. Criteria specify study design, publication date, country, participant characteristics, and other factors.
Search For All Relevant Studies
NESR librarians create a search strategy, using the analytic framework and inclusion and exclusion criteria as guides, to find studies that are relevant to the question. The strategy identifies relevant electronic databases and key search terms. The librarians conduct the search, which yields a list of potentially relevant studies.
NESR analysts screen the potentially relevant studies using the inclusion and exclusion criteria. Studies that meet all of the criteria are included in the systematic review. NESR analysts document the studies that were excluded and why.
NESR analysts extract data that help answer the systematic review question from each included study. Data include:
- Study design
- Participant characteristics
- Funding source
Assess Risk of Bias
NESR analysts use a risk of bias tool to consistently assess how each included study was designed and conducted. The design and conduct of a study impact the accuracy of its results. This assessment provides important information about the included studies that is used throughout the rest of the review.
NESR analysts and the scientific experts synthesize the evidence from all included studies to examine whether the intervention or exposure is related to the outcome in the population of interest. Evidence synthesis involves looking for similarities and differences between the studies and their results, determining whether any factors impact the relationships being examined, and identifying gaps and limitations in the evidence.
Develop a Conclusion Statement
The scientific experts, facilitated by NESR analysts, use the evidence synthesis to carefully develop a conclusion statement. A conclusion statement describes the state of the science, and is written as the answer to the systematic review question. It may also state that there is not enough evidence to answer the question.
Grade the Strength of the Evidence
The scientific experts, facilitated by NESR analysts, use a grading tool to consistently evaluate the risk of bias, consistency, precision, directness, and generalizability of the evidence underlying the conclusion statement. They assign one of four grades to indicate the strength of the evidence:
- Grade not assignable
Recommend Future Research
NESR analysts and external experts recommend future research from any gaps or limitations in the evidence.
NESR ensures that each systematic review is free and available, and that the information can be easily understood by a range of audiences.
Comprehensive information about every systematic review conducted by NESR is published on our website as follows:
- Plain language summary: Provides an overview of each review using concise, non-technical language for a range of readers.
- Technical abstract: Provides a short, structured, technical summary of each review to help readers quickly determine the overall scope, methods, and findings of the review without having to read the entire report.
- Full systematic review: Provides complete documentation of the review
- Methodology: Details the methods used to conduct the systematic review, including who conducted it, the scope, search plan and results, and processes used to extract data, assess risk of bias, synthesize evidence, develop conclusion statements, and grade the strength of evidence.
- Conclusion statement(s) and grade(s): Answer the review question, and provides a grade that represents the strength of evidence supporting that conclusion statement.
- Summary: Provides the key points from the review
- Description of the evidence: Describes the included articles, focusing on subject characteristics, interventions/exposures and outcomes examined, methodology used, and a summary of study results.
- Evidence synthesis: Discusses overall themes in the body of evidence and provides an assessment of the strength of the evidence.
- Research recommendations: Suggests future research based on the gaps and limitations identified in the evidence.
- Included articles: Reference list of articles included in the review.
NESR systematic reviews can be used in a variety of ways by Federal stakeholders, scientists and the research community, and the public. It is important to note that NESR’s reviews end with the development of a graded conclusion statement that describes the state of the science. The systematic review process does not include drawing implications from conclusion statements and conclusion statements are not dietary guidance. In some cases, such as with the Dietary Guidelines Advisory Committee, a separate, subsequent effort involves the development of advice based on the scientific evidence reviewed. For more information about the process for developing the Dietary Guidelines for Americans and the Advisory Committee, visit: www.DietaryGuidelines.gov.
The Nutrition Evidence Systematic Review (NESR) team specializes in conducting food- and nutrition-related systematic reviews.
Roles and Responsibilities
NESR projects are completed in a collaborative manner. Learn more about the roles and responsibilities of the NESR team, scientific expert groups, Federal Stakeholders, the Research Community, and the Public.
Advancing NESR Methodology
NESR works to ensure that our methodology remains state-of-the-art. Learn more about how we continuously advance our methodology.