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I am not sure how I feel about the use of measures of lung function as the basis for low exposure <br />effects (realizing that there ARE data on more obviously significant measures such as hospital <br />admissions). On the one hand, these could be precursors to more clinically significant effects. <br />But they could also be sub-clinical effects with no evident relationship to quality or length of <br />life. I don't believe the current document fully addresses this issue. <br />This is then related to another issue that appears throughout the health effects discussions in the <br />document. The question is raised as to whether effects at low exposures, which one could take to <br />be background, affect the exposure-response relationship at higher exposures. There is a point in <br />the document at which the authors discuss the fact that the exposure-response relationships noted <br />in clinical studies at EPA labs (e.g. here in the Research Triangle Park) might be compromised <br />by the higher annual average ozone levels in the surrounding area. They suggest specifically that <br />subjects may have been desensitized by the background exposures, depressing the exposure- <br />response slope below that expected in other areas of the country, or at least those areas with <br />lower policy relevant background levels. However, there is just as much evidence that low levels <br />of exposure to pollutants don't cause adverse effects directly, but instead sensitize individuals to <br />subsequent exposures to a range of risk factors. This would tend to inflate the exposure-response <br />slopes in the study areas relative to other geographic areas with lower background. The authors <br />just must be clear what they are assuming to be the case here, and provide the evidence to <br />support that claim. <br />A minor quibble is that the authors refer at numerous points to "evidence based" conclusions. I <br />know this is a fashionable phrase, and perhaps they are required to use it by current EPA <br />procedures (although I can't find where this is true), but it leaves the reader wondering what the <br />alterative to "evidence based" conclusions might be. In the medical field, "evidence based" is <br />usually used in contrast to expert judgment by physicians. Is that the intent in this drafr <br />document? <br />Other than these points, I was quite pleased with the draft document. <br />G-° ~~" <br />C-13 <br />