Navidi W
Department of Mathematical and Computer Sciences, Colorado School of Mines, Golden 80401, USA.
Biometrics. 1998 Jun;54(2):596-605.
In the case-crossover design (Maclure, 1991, American Journal of Epidemiology 133, 144-153), only cases are sampled, and risk estimates are based on within-subject comparisons of exposures at failure times with exposures at times prior to failure, using matched case-control methods. While the design provides considerable advantages, unidirectional retrospective control sampling (selecting control times only prior to failure) can cause risk estimates to be confounded by time trends in exposure. However, when subsequent exposures are not influenced by failures, as in studies of environmental exposures such as air pollutants, it is possible to determine at times postfailure what a subject's level of exposure would have been had the subject not failed. We describe a bidirectional case-crossover design in which exposures at failure are compared with exposures both before and after failure. Simulation analyses show that relative risk estimates are resistant to confounding by time trend. We also extend the method to studies involving multiple failure times.
在病例交叉设计中（Maclure，1991年，《美国流行病学杂志》133卷，144 - 153页），仅对病例进行抽样，风险估计基于对失效时间的暴露情况与失效前时间的暴露情况进行个体内比较，采用匹配病例对照方法。虽然该设计具有相当大的优势，但单向回顾性对照抽样（仅在失效前选择对照时间）可能会导致风险估计受到暴露时间趋势的混杂影响。然而，当后续暴露不受失效影响时，如在空气污染物等环境暴露研究中，有可能确定在失效后某一时刻，如果该个体未失效其暴露水平会是多少。我们描述了一种双向病例交叉设计，其中将失效时的暴露与失效前后的暴露进行比较。模拟分析表明，相对风险估计对时间趋势的混杂具有抗性。我们还将该方法扩展到涉及多个失效时间的研究中。
