Skip to main content

Currently Skimming:

6 Overall Conclusions and Recommendations
Pages 160-181

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 160...
... Selection of a health-based standard focuses on the lowest ambient concentration that poses a risk of adverse health effects in the most sensitive population, whereas benefits assessment uses information to estimate all the health-risk reductions in the entire population that is expected to experience a change in ambient concentrations. OZONE MORTALITY EFFECT In carrying out its charge, the committee considered not only the recent epidemiologic evidence, but also toxicologic and pathophysiologic evidence that points to mechanisms by which ozone may contribute to premature mortality.
From page 161...
... ? • Given that age and health status are important in estimating the quantity and quality of the remaining life expectancy, how dependent is the ozonemortality relationship on those and other personal characteristics, such as socioeconomic status?
From page 162...
... Together, low personal exposures and weak relationships between personal exposure concentrations and ambient concentrations suggest that 24-h ambient ozone concentrations are poor proxies for personal exposures. For shorter averaging periods, such as the afternoon (when both personal outdoor activity and ozone concentration can be at their highest)
From page 163...
... Colinearity among ambient pollutants raises concerns about possible confounding of ozone mortality effects by correlated copollutants. The concerns center on the possibility that effects associated with ambient ozone may be the consequences not only of ozone exposure but of correlated pollutants not included in the health-effects model.
From page 164...
... Threshold To characterize the association between daily variations in ambient ozone concentrations and daily variations in deaths, a linear model is used in which it is assumed that the change in mortality risk is constant across pollution concentrations. It is unlikely that the association between exposure and response at the individual level follows that simple mathematical formulation.
From page 165...
... Those results suggest a near-linear association between ambient concentrations of ozone and daily mortality in the United States. Exposure misclassification caused by use of an average of ambient fixed-site monitoring data to estimate population-average personal exposure makes it more difficult to distinguish between linear and threshold models.
From page 166...
... 3 Current economic valuations of mortality are based on study samples that have average remaining life expectancies. It would be problematic to extrapolate these valuations to a circumstance in which the remaining life expectancy of the population most at risk is very short.
From page 167...
... In the absence of knowledge about the amount of time lost because of acute effects, one may hypothesize that air pollutants were able to trigger death only in a pool of very frail people, those already in very bad health. Assuming that the remaining life expectancy of those frail people was very short even in the absence of pollution, the effect of air pollution would consist of only a minor shift of the time of death, namely, a short advancement of death.
From page 168...
... have found small positive effects in warm seasons, but other cohort studies have not found positive associations between long-term average ozone concentrations and cardiopulmonary mortality after controlling for PM2.5. The weak current evidence from cohort studies of an association of premature mortality with chronic exposure to ozone suggests that risks are larger than those observed in acute effects studies alone.
From page 169...
... In light of this recommended approach, future RIAs should give little or no weight to the assumption that there is no causal association between estimated reductions in the incidence of premature mortality and reduced ozone exposure. Effect of Ozone Exposure on Life Expectancy The impact of pollution on mortality may be quantified in terms of changes in mortality rates, number of deaths in a given period, or the months (or years)
From page 170...
... Effects of long-term cumulated exposure are, by design, ignored in those studies. Reductions in life expectancy based on the time-series results can be calculated by using life-table methods, but lack of information about the at-risk population necessitates making the assumption that remaining life expectancy is comparable with of others in the same age-sex cohort.
From page 171...
... As mentioned previously, the current evidence from cohort studies, although it is weak, supports the notion that the effects estimates seen in the-series studies reflect only a portion of the total effect. The question of how to use the epidemiologic information to translate into risk changes and benefits assessment is the subject of debate.
From page 172...
... In its primary benefits estimates, EPA applies the VSL to all lives saved regardless of the age or health status of the population experiencing the change in mortality risk and regardless of the cause of the change. Because there is some expectation that WTP for mortality-risk reduction will vary with the characteristics of the population affected or with the context of the risk change, EPA asked the committee to assess scientific approaches to assigning economic values to reductions in mortality risk associated with ozone reductions and to address the questions of economic valuation for different changes in life expectancy.
From page 173...
... We conclude that the empirical evidence is insufficient to support a specific quantitative adjustment of the WTP estimates to account for differences in remaining life expectancy, but we do not reject the concept that such adjustments may be appropriate. It is plausible that people with shorter remaining life expectancy are willing to devote less of their resources to reducing their mortality risk than would people with longer remaining life expectancy.
From page 174...
... Empirical evidence of how WTP varies with population or risk characteristics is not sufficiently consistent to support a change in this practice that EPA has been using for many years. Estimates of Value of a Statistical Life-Year The use of a constant VSLY in the valuation of increases in life expectancy requires the assumption that WTP values for mortality risk reductions be consistently declining with increasing age.
From page 175...
... That is because greater mortality risk associated with ozone appears to be in the elderly population and because latent risk may be involved. Given this population's substantially less than average remaining life expectancy, it is possible that its WTP to reduce mortality risk would be less than the average WTP for the population as a whole.
From page 176...
... and the future research needs for valuation (from Chapter 5) briefly summarized in this section should be addressed as part of EPA's research strategy for estimating the benefits of reducing ambient ozone.
From page 177...
... Monitor ozone in winter and report the measurements. The size of the winter program should be sufficient to allow researchers to examine seasonal differences in risk, how the differences vary spatially between communities with warmer and cooler winters, and ozone-mortality relationships at lower ozone concentrations.
From page 178...
... Recommendations for Future Research on Valuation Explore how WTP varies with mortality-risk changes and changes in life expectancy, and explore how WTP varies with population characteristics such as age, health status, and baseline risk levels. Although the research needs would be addressed primarily by using stated-preference methods, explore ways to address research needs with further developments of revealedpreference methods.
From page 179...
... Make datasets available for meta-analysis by urging researchers who receive EPA funding to make their datasets available for meta-analyses in addition to providing their published results. Explore and develop full life-cycle methods for communicating and valuing changes in mortality risk as a shift in the survival curve, which plots survival probabilities in all future periods and from which life expectancy is derived.
From page 180...
... It is the committee's judgment that the available evidence is not sufficient to support such a change at this time, but alternative approaches should be explored in sensitivity analyses and further research should be conducted to answer the questions raised about the validity of EPA's current approach. As new information emerges on population characteristics of those susceptible to mortality from ozone and on variations in WTP for mortality-risk reductions (or increases in life expectancy)
From page 181...
... For example, this report has indicated where there is a greater understanding of many aspects of PMmortality relationships relative to those for ozone. Continued enhancement of knowledge and methods for valuation of ozone mortality risk reduction benefits will inform future regulatory decision making and help in understanding the relative importance and value of effects caused by various pollutants.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.