Department of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA.
Alzheimer Dis Assoc Disord. 2012 Oct-Dec;26(4):300-6. doi: 10.1097/WAD.0b013e3182420b6e.
If smoking is a risk factor for Alzheimer disease (AD) but a smoker dies of another cause before developing or manifesting AD, smoking-related mortality may mask the relationship between smoking and AD. This phenomenon, referred to as competing risk, complicates efforts to model the effect of smoking on AD. Typical survival regression models assume that censorship from analysis is unrelated to an individual's probability for developing AD (ie, censoring is noninformative). However, if individuals who die before developing AD are younger than those who survive long enough to develop AD, and if they include a higher percentage of smokers than nonsmokers, the incidence of AD will appear to be higher in older individuals and in nonsmokers. Further, age-specific mortality rates are higher in smokers because they die earlier than nonsmokers. Therefore, if we fail to take into account the competing risk of death when we estimate the effect of smoking on AD, we bias the results and are in fact only comparing the incidence of AD in nonsmokers with that in the healthiest smokers. In this study, we demonstrate that the effect of smoking on AD differs in models that are and are not adjusted for competing risks.
如果吸烟是阿尔茨海默病（AD）的一个风险因素，但一个吸烟者因其他原因死亡，在出现或表现出 AD 之前，与吸烟相关的死亡率可能掩盖了吸烟与 AD 之间的关系。这种现象被称为竞争风险，使吸烟对 AD 影响的建模工作变得复杂。典型的生存回归模型假设分析中的删失与个体患 AD 的概率无关（即删失是无信息的）。然而，如果在出现 AD 之前死亡的个体比那些存活时间足够长以出现 AD 的个体年轻，并且如果他们比不吸烟者包含更高比例的吸烟者，那么在年龄较大的个体和不吸烟者中，AD 的发病率似乎会更高。此外，吸烟者的特定年龄死亡率较高，因为他们比不吸烟者更早死亡。因此，如果我们在估计吸烟对 AD 的影响时未能考虑到死亡的竞争风险，我们会产生偏差，实际上我们只是在比较不吸烟者和最健康的吸烟者中 AD 的发病率。在这项研究中，我们证明了在考虑和不考虑竞争风险的模型中，吸烟对 AD 的影响是不同的。
