Division of Epidemiology, Statistics, and Prevention Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20854, USA.
Paediatr Perinat Epidemiol. 2013 Sep;27(5):491-502. doi: 10.1111/ppe.12073.
Selection is a common problem in paediatric and perinatal epidemiology, and truncation can be thought of as missing person time that can result in selection bias. Left truncation, also known as late or staggered entry, may induce selection bias and/or adversely affect precision. There are two kinds of left truncation: fixed left truncation where the start of follow-up is initiated at a set time, and variable left truncation where follow-up begins at a stochastically varying time-point.
Using data from a time-to-pregnancy study, augmented by a simulation study, we demonstrate the effects of fixed and variable truncation on estimates of the hazard ratio.
First, fixed or variable non-differential left truncation results in a loss of precision. Fixed or variable differential left truncation results in a bias either towards or away from the null as well as a loss of precision. The extent and direction of this bias is a function of the size and direction of the association between exposure and outcome, and occurs in common scenarios and under a wide range of conditions.
As demonstrated in simulation studies, selection bias due to left truncation could have a serious impact on inferences, especially in the case of fixed or variable differential left truncation. When present in epidemiologic studies, proper accounting for left truncation is just as important as proper accounting for right censoring.
选择是儿科和围产流行病学中的常见问题，截尾可以被视为缺失的个体时间，可能导致选择偏倚。左截断，也称为晚期或交错进入，可能会引起选择偏差和/或对精度产生不利影响。左截断有两种类型：固定左截断，其中随访的开始时间设定在一个固定的时间；和可变左截断，其中随访开始时间是随机变化的。
使用来自妊娠时间研究的数据，并通过模拟研究进行扩充，我们展示了固定和可变截断对危险比估计的影响。
首先，固定或可变的非差异左截断会导致精度损失。固定或可变的差异左截断会导致向零值或远离零值的偏差，以及精度损失。这种偏差的程度和方向是暴露与结局之间关联的大小和方向的函数，在常见的情况下和广泛的条件下都会发生。
正如模拟研究所示，由于左截断引起的选择偏差可能对推断产生严重影响，特别是在固定或可变的差异左截断的情况下。在流行病学研究中，正确处理左截断和正确处理右删失一样重要。
