Limits...
The effect of dose and timing of dose on the association between airborne particles and survival.

Schwartz J, Coull B, Laden F, Ryan L - Environ. Health Perspect. (2008)

Bottom Line: Because the uncertainties around the resultant curve do not reflect the uncertainty in model choice, we also used model averaging as an alternative approach, where multiple models are fit explicitly and averaged, weighted by their probability of being correct given the data.We examined the lag relationship by model averaging across a range of unconstrained distributed lag models.Reduction in particle concentrations below U.S. EPA standards would increase life expectancy.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health, Harvard School of Public Health, 401 Park Dr., Suite 415 W, P.O. Box 15698, Boston, MA 02215 USA. jschwrtz@hsph.harvard.edu <jschwrtz@hsph.harvard.edu>

ABSTRACT

Background: Understanding the shape of the concentration-response curve for particles is important for public health, and lack of such understanding was recently cited by U.S. Environmental Protection Agency (EPA) as a reason for not tightening the standards. Similarly, the delay between changes in exposure and changes in health is also important in public health decision making. We addressed these issues using an extended follow-up of the Harvard Six Cities Study.

Methods: Cox proportional hazards models were fit controlling for smoking, body mass index, and other covariates. Two approaches were used. First, we used penalized splines, which fit a flexible functional form to the concentration response to examine its shape, and chose the degrees of freedom for the curve based on Akaike's information criterion. Because the uncertainties around the resultant curve do not reflect the uncertainty in model choice, we also used model averaging as an alternative approach, where multiple models are fit explicitly and averaged, weighted by their probability of being correct given the data. We examined the lag relationship by model averaging across a range of unconstrained distributed lag models.

Results: We found that the concentration-response curve is linear, clearly continuing below the current U.S. standard of 15 microg/m3, and that the effects of changes in exposure on mortality are seen within two years.

Conclusions: Reduction in particle concentrations below U.S. EPA standards would increase life expectancy.

Show MeSH

Related in: MedlinePlus

The model-averaged estimated effect of a 10-μg/m3 increase in PM2.5 on all-cause mortality at different lags (in years) between exposure and death. Each lag is estimated independently of the others. Also shown are the pointwise 95% CIs for each lag, based on jacknife estimates.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2199297&req=5

f4-ehp0116-000064: The model-averaged estimated effect of a 10-μg/m3 increase in PM2.5 on all-cause mortality at different lags (in years) between exposure and death. Each lag is estimated independently of the others. Also shown are the pointwise 95% CIs for each lag, based on jacknife estimates.

Mentions: Table 3 shows the 11 candidate models for the distributed lag modeling, formed by considering different numbers of lags, and their posterior probabilities. Figure 4 shows the estimated relative risk (and 95% CI) for the effect of a 10-μg/m3 increase in PM2.5 in the year of death, the year preceding death, and so on, up to the 5 years preceding death. The increased risk of death associated with PM2.5 is essentially all manifested within 2 years of exposure.


The effect of dose and timing of dose on the association between airborne particles and survival.

Schwartz J, Coull B, Laden F, Ryan L - Environ. Health Perspect. (2008)

The model-averaged estimated effect of a 10-μg/m3 increase in PM2.5 on all-cause mortality at different lags (in years) between exposure and death. Each lag is estimated independently of the others. Also shown are the pointwise 95% CIs for each lag, based on jacknife estimates.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2199297&req=5

f4-ehp0116-000064: The model-averaged estimated effect of a 10-μg/m3 increase in PM2.5 on all-cause mortality at different lags (in years) between exposure and death. Each lag is estimated independently of the others. Also shown are the pointwise 95% CIs for each lag, based on jacknife estimates.
Mentions: Table 3 shows the 11 candidate models for the distributed lag modeling, formed by considering different numbers of lags, and their posterior probabilities. Figure 4 shows the estimated relative risk (and 95% CI) for the effect of a 10-μg/m3 increase in PM2.5 in the year of death, the year preceding death, and so on, up to the 5 years preceding death. The increased risk of death associated with PM2.5 is essentially all manifested within 2 years of exposure.

Bottom Line: Because the uncertainties around the resultant curve do not reflect the uncertainty in model choice, we also used model averaging as an alternative approach, where multiple models are fit explicitly and averaged, weighted by their probability of being correct given the data.We examined the lag relationship by model averaging across a range of unconstrained distributed lag models.Reduction in particle concentrations below U.S. EPA standards would increase life expectancy.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health, Harvard School of Public Health, 401 Park Dr., Suite 415 W, P.O. Box 15698, Boston, MA 02215 USA. jschwrtz@hsph.harvard.edu <jschwrtz@hsph.harvard.edu>

ABSTRACT

Background: Understanding the shape of the concentration-response curve for particles is important for public health, and lack of such understanding was recently cited by U.S. Environmental Protection Agency (EPA) as a reason for not tightening the standards. Similarly, the delay between changes in exposure and changes in health is also important in public health decision making. We addressed these issues using an extended follow-up of the Harvard Six Cities Study.

Methods: Cox proportional hazards models were fit controlling for smoking, body mass index, and other covariates. Two approaches were used. First, we used penalized splines, which fit a flexible functional form to the concentration response to examine its shape, and chose the degrees of freedom for the curve based on Akaike's information criterion. Because the uncertainties around the resultant curve do not reflect the uncertainty in model choice, we also used model averaging as an alternative approach, where multiple models are fit explicitly and averaged, weighted by their probability of being correct given the data. We examined the lag relationship by model averaging across a range of unconstrained distributed lag models.

Results: We found that the concentration-response curve is linear, clearly continuing below the current U.S. standard of 15 microg/m3, and that the effects of changes in exposure on mortality are seen within two years.

Conclusions: Reduction in particle concentrations below U.S. EPA standards would increase life expectancy.

Show MeSH
Related in: MedlinePlus