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Dose–Response Models are Conditional on Determination of Causality

Causality is a key underlying issue in this special collection of articles regarding uncertainties in health risk estimates for “criteria” air pollutants in the United States and estimates of human health benefits of the National Ambient Air Quality Standards (NAAQS). Specifically, does exposure to a particular air pollutant at a particular concentration cause an adverse effect in the exposed population? However, before addressing this question, some context is required. It is not possible to discuss the risk assessment process related to the NAAQS without consideration of the legal and policy context of these standards. Therefore, some of this context is provided here. There is also a critical distinction between how information is used to inform the process of revising or setting a standard versus how it is used in benefit-cost assessment. The statutory mandate for the NAAQS is from the Clean Air Act (CAA). The CAA requires the Administrator of the U.S. Environmental Protection Agency to list those air pollutants that “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.” These pollutants are referred to as “criteria pollutants.” Here, we will focus on NAAQS aimed at protecting public health, which are referred to as “primary” standards. The legislative and historical backgrounds for NAAQS are described in the U.S. Environmental Protection Agency’s (EPA’s) policy assessment for each of the pollutants regulated under the NAAQS. For example, see the ozone policy assessment for more details.(1) Section 109(b)(1) of the CAA directs that a primary standard allows “an adequate margin of safety” and be “requisite to protect the public health.” This language is vague but has been interpreted as the re-