Population Studies Division, Health Canada, Ottawa, ON, Canada.
Int J Occup Med Environ Health. 2011 Sep;24(3):249-55. doi: 10.2478/s13382-011-0034-y. Epub 2011 Aug 16.
The objective of this study was to investigate variants of case-crossover design for assessing correlations between counts of health events over time and exposure to ambient air pollution. For illustrative purposes, daily emergency department (ED) visits for depression among females were considered.
Ambient nitrogen dioxide (NO(2)) was used as a principal ambient air pollutant. In addition, sulphur dioxide (SO(2)) and carbon monoxide (CO) were considered. Different configurations of the control periods (every 1, 2, …, 10 days) and different forms (linear, natural splines) of meteorological factors in the applied conditional logistic regression models were used. The sequence of overlapping age intervals was defined ([0, 19], [1, 20], and so on) and each age group was analyzed separately. The results for the defined age sequences allow identifying age ranges in which the effects are strongest.
Consequently, for example, different age ranges for patients for which ED visits for depression were correlated with NO(2) and SO(2) were identified. This age-interval difference explains the very often observed phenomenon whereby two air pollutants used in one model may not show correlations with health outcomes. In this situation they affect separate age groups. The results also show dependency on number-defined control periods for the applied case-crossover technique. The opposite statistical conclusions may be generated by using different control schemas.
The results support the hypothesis that ED visits for depressive disorder may be correlated with exposure to ambient air pollution.
本研究旨在探讨病例交叉设计的变体，以评估随时间推移的健康事件计数与暴露于环境空气污染之间的相关性。为了说明问题，考虑了女性每日因抑郁症到急诊室（ED）就诊的情况。
环境二氧化氮（NO2）被用作主要的环境空气污染物。此外，还考虑了二氧化硫（SO2）和一氧化碳（CO）。在应用条件逻辑回归模型中，使用了不同的对照期（每 1、2、...、10 天）配置和不同形式（线性、自然样条）的气象因素。重叠年龄区间的顺序被定义为[0,19]、[1,20]等），并分别分析每个年龄组。定义年龄序列的结果允许确定效应最强的年龄范围。
因此，例如，确定了与 NO2 和 SO2 相关的 ED 就诊的抑郁症患者的不同年龄范围。这种年龄区间差异解释了经常观察到的现象，即一个模型中使用的两种空气污染物可能与健康结果没有相关性。在这种情况下，它们会影响不同的年龄组。结果还表明，应用病例交叉技术时，需要定义数量的对照期。使用不同的控制方案可能会产生相反的统计结论。
结果支持 ED 就诊因抑郁障碍与暴露于环境空气污染有关的假设。
