What Characteristics of Epidemiologic Evidence Correlate with Study Usefulness or Influence? Experiences in Three Settings

Abstract

BACKGROUND AND AIM: Epidemiologic studies play key roles in: 1) environmental chemical risk assessment for setting regulatory standards (US EPA, US states, countries around the globe); and 2) determinations by authoritative bodies (National Academies of Medicine and Science, California Proposition 65 committees, and IARC) that advise on the strength of evidence for present or potential harm to human health and that may be asked to make recommendations. Drawing on experiences in both types of settings, and in an organization that seeks to move environmental health science into the real world, this presentation demonstrates how specific studies become influential. METHODS: Concepts are discussed and will be illustrated through examples (pesticides, cadmium, tetrachlorodibenzo(p)dioxin, radiation; cognitive impairment, lung or breast cancer). RESULTS:For regulatory agencies, epidemiology can play a role in hazard identification, exposure assessment, risk assessment, and risk characterization. In this context, two key features determine the utility of epidemiologic studies: overall quality and rigor; and presence of quantitative exposure measures linked to health outcomes, preferably allowing estimation of an exposure-response relationship. By contrast, panels of the National Academies, IARC, and California Proposition 65 Committees are generally tasked with reviewing a body of research and reaching consensus on the evidence for causal associations between specific exposures and defined health outcomes or on whether exposure prevalence or levels pose a threat to human health. They may also be mandated to provide recommendations. The last setting, Project TENDR (Targeting Environment and NeuroDevelopmental Risks), is more similar in its purpose to authoritative bodies than to risk assessment, but more similar to risk assessment in being directed towards policy or action. CONCLUSIONS:The overarching goals of the program, agency, or panel will determine what study attributes are most valued. The amount, quality and types of evidence will also determine usefulness of epidemiologic studies. Finally, the desirable characteristics may be exposure- or outcome-specific. KEYWORDS: environmental epidemiology, methodology study design, policy and practice