The European Food Safety Authority (EFSA) is developing a guidance document on the use of the Weight of evidence approach in scientific assessments applicable to all areas under EFSA’s remit.
It addresses the use of the weight of evidence applying both qualitative and quantitative approaches. In developing the guidance, the WG took into account related European and international activities to ensure consistency and harmonisation of methodologies.
This guidance document is intended to guide EFSA panels and staff on the use of the weight of evidence approach in scientific assessments. It provides a flexible framework within which experts can apply those methods which most appropriately fit the purpose of their individual assessment.
Weight of evidence assessment is a process in which evidence is assembled, evaluated with regard to its potential contribution to addressing a question, and integrated to determine the relative support for possible answers to the assessment question. The document considers the weight of evidence assessment as comprising three basic steps: 1. assembling the evidence, 2. weighing the evidence, 3. integrating the evidence.
The present document defines reliability, relevance and consistency, in terms of their contributions to the weight of evidence assessment: Reliability is the extent to which the information comprising a line of evidence is correct. Relevance is the contribution a line of evidence would make to answer a specified question, if the information comprising the line of evidence was correct. Consistency is the extent to which the contributions of different lines of evidence to answering the specified question are compatible.
While no single approach is prescribed, pointers towards available methodologies are provided together with criteria for selecting the most appropriate one for individual assessments.
Reporting should be consistent with EFSA’s general principles regarding transparency and reporting. In a weight of evidence assessment this should include justifying the choice of methods used, documenting all steps of the procedure in sufficient detail for them to be repeated, and making clear where and how expert judgement has been used. Reporting should also include referencing and, if appropriate, listing or summarising all evidence considered, identifying any evidence that was excluded; detailed reporting of the conclusions; and sufficient information on intermediate results for readers to understand how the conclusions were reached.
Several case studies covering the various areas under EFSA’s remit are annexed to the guidance document to illustrate the applicability of the proposed approach.