Schwartz Joel, Coull Brent, Laden Francine, Ryan Louise
Department of Environmental Health, Harvard School of Public Health, 401 Park Dr., Suite 415 W, P.O. Box 15698, Boston, MA 02215 USA.
Environ Health Perspect. 2008 Jan;116(1):64-9. doi: 10.1289/ehp.9955.
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.
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.
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.
Reduction in particle concentrations below U.S. EPA standards would increase life expectancy.
了解颗粒物浓度 - 反应曲线的形状对公共卫生很重要，美国环境保护局（EPA）最近指出，缺乏这种认识是未收紧标准的一个原因。同样，暴露变化与健康变化之间的延迟在公共卫生决策中也很重要。我们通过对哈佛六城市研究的延长随访来解决这些问题。
拟合Cox比例风险模型，对吸烟、体重指数和其他协变量进行控制。使用了两种方法。首先，我们使用惩罚样条，它对浓度反应拟合一种灵活的函数形式以检查其形状，并根据赤池信息准则选择曲线的自由度。由于所得曲线周围的不确定性不能反映模型选择中的不确定性，我们还使用模型平均作为替代方法，即明确拟合多个模型并进行平均，根据给定数据其正确的概率加权。我们通过对一系列无约束分布滞后模型进行模型平均来研究滞后关系。
我们发现浓度 - 反应曲线是线性的，明显在当前美国15微克/立方米的标准以下持续，并且暴露变化对死亡率的影响在两年内可见。
将颗粒物浓度降低到美国EPA标准以下将增加预期寿命。
