REPORT OF THE MASSACHUSETTS WEIGHT-OF-EVIDENCE WORKGROUP - A WEIGHT-OF-EVIDENCE APPROACH FOR EVALUATING ECOLOGICAL RISKS

Weight-of-evidence is the process by which multiple measurement endpoi nts are related to an assessment endpoint to evaluate whether signific ant risk of harm is posed to the environment. In this paper, a methodo logy is offered for reconciling or balancing multiple lines of evidenc e pertaining to an assessment endpoint. Weight-of-evidence is reflecte d in three characteristics of measurement endpoints: (a) the weight as signed to each measurement endpoint; (b) the magnitude of response obs erved in the measurement endpoint; and (c) the concurrence among outco mes of multiple measurement endpoints. First, weights are assigned to measurement endpoints based on attributes related to: (a) strength of association between assessment and measurement endpoints; (b) data qua lity; and (c) study design and execution. Second, the magnitude of res ponse in the measurement endpoint is evaluated with respect to whether the measurement endpoint indicates the presence or absence of harm; a s well as the magnitude. Third, concurrence among measurement endpoint s is evaluated by plotting the findings of the two preceding steps on a matrix for each measurement endpoint evaluated. The matrix allows ea sy visual examination of agreements or divergences among measurement e ndpoints, facilitating interpretation of the collection of measurement endpoints with respect to the assessment endpoint. A qualitative adap tation of the weight-of-evidence approach is also presented.