Evidence Synthesis of Observational Studies in Environmental Health: Lessons Learned from a Systematic Review on Traffic-Related Air Pollution

• Type of Material: Article
• Authors: Hanna Boogaard, Health Effects Institute; Richard W. Atkinson, St. George's University of London; Jeffrey R. Brook, University of Toronto; Howard Chang, Emory University; Gerard Hoek, Utrecht University; Barbara Hoffmann, University of Düsseldorf; Sharon K. Sagiv, University of California, Berkeley; Evangelia Samoli, National and Kapodistrian University of Athens; Audrey Smargiassi, University of Montreal; Adam A. Szpiro, University of Washington; Danielle Vienneau, University of Basel; Jennifer Weuve, Boston University; Frederick W. Lurmann, Sonoma Technology, Inc.; Francesco Forastiere, Imperial College London
• Language: English
• Date: 2023-11-22
• Publisher: EHP Publishing
• Publication Version: Final Published Version
• Copyright Statement: EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted.
• Final Published Version (URL): https://doi.org/10.1289/EHP11532
• Title of Journal or Parent Work: Environmental Health Perspectives: Commentary
• Volume: 131
• Issue: 11
• Start Page: 115002
• Grant/Funding Information: Research described in this article was conducted under contract to the HEI, an organization jointly funded by the United States Environmental Protection Agency (assistance award no. CR-83998101) and certain motor vehicle and engine manufacturers.
• Keywords: air pollution; Office of Health Assessment and Translation; Grading of Recommendations Assessment, Development, and Evaluation; traffic
• Research Categories: Environmental Sciences; Health Sciences, Public Health; Health Sciences, Epidemiology

Abstract

Background: There is a long tradition in environmental health of using frameworks for evidence synthesis, such as those of the U.S. Environmental Protection Agency for its Integrated Science Assessments and the International Agency for Research on Cancer Monographs. The framework, Grading of Recommendations Assessment, Development, and Evaluation (GRADE), was developed for evidence synthesis in clinical medicine. The U.S. Office of Health Assessment and Translation (OHAT) elaborated an approach for evidence synthesis in environmental health building on GRADE. Methods: We applied a modified OHAT approach and a broader “narrative” assessment to assess the level of confidence in a large systematic review on traffic-related air pollution and health outcomes. Discussion: We discuss several challenges with the OHAT approach and its implementation and suggest improvements for synthesizing evidence from observational studies in environmental health. We consider the determination of confidence using a formal rating scheme of up- and downgrading of certain factors, the treatment of every factor as equally important, and the lower initial confidence rating of observational studies to be fundamental issues in the OHAT approach. We argue that some observational studies can offer high-confidence evidence in environmental health. We note that heterogeneity in magnitude of effect estimates should generally not weaken the confidence in the evidence, and consistency of associations across study designs, populations, and exposure assessment methods may strengthen confidence in the evidence. We mention that publication bias should be explored beyond statistical methods and is likely limited when large and collaborative studies comprise most of the evidence and when accrued over several decades. We propose to identify possible key biases, their most likely direction, and their potential impacts on the results. We think that the OHAT approach and other GRADE-type frameworks require substantial modification to align better with features of environmental health questions and the studies that address them. We emphasize that a broader, “narrative” evidence assessment based on the systematic review may complement a formal GRADE-type evaluation. https://doi.org/10.1289/EHP11532