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Public Health
Expert opinion

Memorandum on weight of evidence and uncertainties - Revision 2018

Final Opinion


WG on Weigh of Evidence
SCHEER members: Ana Proykova, Renate Krätke, Roberto Bertollini, Teresa Borges, Raquel Duarte-Davidson, Demosthenes Panagiotakos, Rémy Slama, Marian Scott, Emanuela Testai, Theo Vermeire, Marco Vighi
SCHER and SCENIHR members (2013-2016): Alena Bartonova, Claire Beausoleil, Teresa Fernandes, Jan Linders, Greta Schoeters, Philippe Hartemann
On request from: European Commission
Adopted on: 26 June 2018

Content of the Opinion

This Memorandum is focussed on how to use the weight of evidence approach (WoE) to conduct a risk assessment for stressors to which humans and/or the environment may be exposed. It is intended to complement the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) report on the identification of emerging issues and the work on the challenges in future risk assessment. The aim of this document is to support the use of the WoE, wherever appropriate, for the risk assessment activities of the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER). In addition, it should support the consistency in the work of different EU bodies performing risk assessments. Scientific evidence consists of observations, experimental and model results and expert judgements that serve to support, refute, or modify a scientific hypothesis or theory. The search for relevant information and data for the SCHEER comprises of identifying, collecting and selecting possible sources of evidence in order to perform a risk assessment and/or to answer the specific questions being asked. According to the issue being addressed, the SCHEER may utilise data provided by the DG tasking the SCHEER, or provided by a third party (e.g. stakeholder reports, submissions such as confidential data provided by companies or applicants), reports and Opinions of other scientific, governmental or international bodies, scientific (peer-reviewed) publications, meta-analysis and systematic reviews or personal communications.

The WoE is an iterative process involving:

- Problem formulation
- Identification, collection and selection of the possible sources of evidence
- Assessment and weighing of individual lines of evidence
- Integration of lines of evidence
- Description of uncertainties
- Conclusion and reporting

For each line of evidence, the criteria of validity, reliability and relevance need to be applied and the overall quality has to be assessed. Several tools for the analysis and description of uncertainties are presented. In the integration of the different lines of evidence, the strength of the overall evidence depends on the consistency and the quality of the results. The weighing of the total evidence should be presented in a standard format. A system is proposed that classifies results of analysis for human and environmental risks in terms of:

- Strong weight of evidence: Coherent evidence from a primary line of evidence (human, animal, environment) and one or more other lines of evidence (in particular mode/mechanistic studies) in the absence of conflicting evidence from one of the other lines of evidence (no important data gaps)
- Moderate weight of evidence: good evidence from a primary line of evidence but evidence from several other lines is missing (important data gaps)
- Weak weight of evidence: weak evidence from the primary lines of evidence (severe data gaps)
- Uncertain weight of evidence: due to conflicting information from different lines of evidence that cannot be explained in scientific terms
- Weighing of evidence not possible: No suitable evidence available

Keywords (for literature search):

human health risk assessment, environmental risk assessment, scientific literature, risk analysis, uncertainty and variability analysis, weight-of-evidence/weighing of evidence, data integration, lines of evidence/line of evidence, levels of evidence/level of evidence, strength of evidence/strengths of evidence, quality of evidence, quality criteria, evidence integration/integration of evidence

Opinion to be cited as:

SCHEER (Scientific Committee on Health, Environmental and Emerging Risks), Memorandum on weight of evidence and uncertainties – revision 2018, 26 June 2018.


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