Preamble to the Integrated Science Assessments (ISA)

The Preamble to the Integrated Science Assessments, or "Preamble", is an overview document outlining the basic steps and criteria used in developing the Integrated Science Assessments (ISA). Previously included as part of the ISA, it will now be referenced by each ISA as a stand-alone companion document. Details and considerations specific to an individual ISA will continue to be included in the Preface and introductory material for each ISA. The Preamble and the approach described therein may be refined periodically in consideration of advice and comments received from the Clean Air Scientific Advisory Committee (CASAC) and the public during subsequent reviews of the National Ambient Air Quality Standards (NAAQS).

The Preamble describes the process of searching the literature, selecting studies for consideration, evaluating study quality, synthesizing and integrating the evidence, and characterizing the evidence for public health and welfare impacts of criteria air pollutants. Considerations pertaining to specific disciplines, such as atmospheric science, toxicology, epidemiology, and aquatic and terrestrial ecology are included in the Preamble.

The Preamble also describes the five-level causal framework for evaluating weight of evidence and drawing scientific conclusions and causal judgments.
The five categories are:
  • causal relationship;
  • likely to be a causal relationship;
  • suggestive of, but not sufficient to infer, a causal relationship;
  • inadequate to infer the presence or absence of a causal relationship; and
  • not likely to be a causal relationship.


U.S. EPA. Preamble to the Integrated Science Assessments (ISA). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/067, 2015.

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.