tors, such as exposure considerations and outcomes, will also play a role in selection.

Consideration of the quality of an assessment is predicated on not only its content but the process by which it was prepared. There should be a preassessment discussion of problem formulation and issue identification that indicates the extent of reliance on previous reviews, the focus of the future effort, and the specific issues on which the assessment is likely to be focused. (Guidance on the design of a risk assessment in its formative stages is provided by the NRC [2009].) That would serve as a basis for soliciting external multidisciplinary input at an early stage in such critical matters as mode of action and evaluation of information on specific end points (including both toxicologic and epidemiologic data). It would include a priori delineation and weighting of criteria for evidence of hazard and options analysis for dose-response assessment and associated uncertainties. Attention to specifying evaluation criteria and the options considered is expected to contribute considerably to transparency in the separation of science judgment from science-policy choices.

To increase transparency, accountability, and defensibility and to improve the content and process of assessments, the committee offers the following recommendations regarding future assessments of tetrachloroethylene:

  • The nature of, timeframe for, and extent of consideration of relevant data should be clearly framed and stated (for example, standard searching of identified electronic sources with criteria specified, cutoff date past which no additional data were considered, and identification of current studies by reviewers).

  • Exclusion criteria for particular studies should be clearly identified and explained (for example, unpublished or published after a particular date). In particular, there should be description of steps taken to ensure that studies identified after the original search were selected without bias from the totality of the available data.

  • The methods used for qualitative characterization of uncertainties should be clearly identified, explained, and documented. Qualitative assessment of uncertainty involves (WHO 2008) evaluation of the level of uncertainty of each specified source according to a scoring method, identification and description of the major sources of uncertainty, appraisal of the knowledge base associated with each major source of uncertainty, identification of controversial sources of uncertainty, evaluation of the subjectivity of choices of controversial sources of information, and iteration until the output reflects the current state of knowledge.

  • The specific nature of the process of preparing and reviewing the assessment—including identification of authors and reviewers, timeline and nature of peer input, consultation, and peer review—should be set forth.

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