The Synthesising Epidemiology Evidence Subgroup (SEES) of the COT and Committee on Carcinogenicity (COC) was set up in 2015. Its aim was to review and document current practice, given recent international and national development of methods by which evidence is synthesised, and to make recommendations for COT/COC guidance.
Human studies can provide direct evidence of health impacts of particular exposures. However, much of the evidence comes from observational epidemiological studies, where control of chance, bias (including exposure misclassification) and confounding may be problematic. Systematic review and meta-analysis are gold standard methods for combining epidemiological studies, but may not be available, or practical or possible to conduct for many of the questions considered by COT/COC.
Epidemiological reviews leading to statements or opinions in the last 10 years by COT/COC were identified and reviewed. A wide range of topics were identified relating to infant feeding, alcohol consumption, asbestos exposure, organophosphate exposure and vitamin E intake. The review methods used by the Committees varied by topic and requirement.
Evidence synthesis in the World Health Organization (WHO), the International Agency for Research on Cancer (IARC) and European Food Safety Authority (EFSA) was discussed and a number of well documented major systems for evidence synthesis were reviewed. SEES also considered evidence synthesis methodologies and tools available in order to draw up guidance points for scoping, conducting and reporting. Quality assessment of studies was considered an integral part of review and a large number of numerical scoring tools are available. Specific issues related to quantitative risk assessment and meta-analysis were identified. Documentation of uncertainty and of (potential conflict of) interests was considered important.
SEES also considered methods for combining epidemiological and toxicological evidence. These are less well developed than those for systematic review, particularly in a quantitative framework. There are currently international initiatives in this area and COT/COC will need to keep this methodological area under regular review