Weight of Evidence: A Review of Concept and Methods

Abstract

"Weight of evidence" (WOE) is a common term in the published scientific and policy-making literature, most often seen in the context of risk assessment (RA). Its definition, however, is unclear. A systematic review of the scientific literature was undertaken to characterize the concept. For the years 1994 through 2004, PubMed was searched for publications in which "weight of evidence" appeared in the abstract and/or title. Of the 276 papers that met these criteria, 92 were selected for review: 71 papers published in 2003 and 2004 (WOE appeared in abstract/title) and 21 from 1994 through 2002 (WOE appeared in title). WOE has three characteristic uses in this literature: (1) metaphorical, where WOE refers to a collection of studies or to an unspecified methodological approach; (2) methodological, where WOE points to established interpretative methodologies (e.g., systematic narrative review, meta-analysis, causal criteria, and/or quality criteria for toxicological studies) or where WOE means that "all" rather than some subset of the evidence is examined, or rarely, where WOE points to methods using quantitative weights for evidence; and (3) theoretical, where WOE serves as a label for a conceptual framework. Several problems are identified: the frequent lack of definition of the term "weight of evidence," multiple uses of the term and a lack of consensus about its meaning, and the many different kinds of weights, both qualitative and quantitative, which can be used in RA. A practical recommendation emerges: the WOE concept and its associated methods should be fully described when used. A research agenda should examine the advantages of quantitative versus qualitative weighting schemes, how best to improve existing methods, and how best to combine those methods (e.g., epidemiology's causal criteria with toxicology's quality criteria).

USEtox characterisation factors for textile chemicals based on a transparent data source selection strategy

“…In step III, for parameters where experimental data of MDQ were not available, a weight-of-evidence (WoE) approach was used (as a method to include all evidence, see, e.g. Weed (2005)), combining estimated data from the application of QSAR or other estimation methods with experimental data from step II. CFs based on estimated data cannot reach MDQ unless supported by some experimental data.…”

Leveraging Big Data Tools and Technologies: Addressing the Challenges of the Water Quality Sector

“…It is also necessary to use a risk assessment method able to integrate different sources of decision process and the expert judgement. In this case, Weight of Evidence has been proven useful in environmental risk assessment [74][75][76][77], and its use in combination with Big Data techniques will allow a holistic approach able to assist decision makers in the process of risk assessment.…”

Expert Review for GHS Classification of Chemicals on Health Effects

“…The term WOE does neither constitute a scientifically well-defined term nor an agreed formalized concept characterized by defined tools and procedures. It is not clear which methods may be used, how they may be applied to the scientific evidence, what the results might be and how these may be used to make decisions in a specific hazard identification 14,15) . The issues of a WOE approach in GHS classification include: i) application of WOE depends on the expertise of experts; ii) there are no canonical frameworks for weighting scientific evidence; iii) a process methodology is low on transparency and high on subjectivity; iv) WOE is usually applied in the case where there is no conclusive single study in demonstrating a cause-effect relationship; v) WOE looks like a 'seat-of-the pants' qualitative assessment.…”

“…Generally, three objectives of the WOE approach are suggested for regulatory decision-making: i) provision of a "clear and transparent framework" for evaluation of the evidence in risk determination; ii) offer of a consistent and standardized approach to evaluating toxic substances submitted to regulatory agencies; and iii) help of identification of the discretionary assumptions in risk determinations from experts [12][13][14] . The GHS defines WOE as follows 2) : "All available information bearing on the determination of toxicity is considered together, including the results of valid in vitro tests, relevant animal data, and human experience such as epidemiological and clinical studies and well-documented case reports and observations.…”