Sjölander Arvid
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm Nobels väg 12, 171 77 Stockholm, Sweden.
Stat Med. 2009 Feb 15;28(4):558-71. doi: 10.1002/sim.3493.
In epidemiological studies we often want to learn about the direct effect of an exposure on an outcome, i.e. the effect that is not relayed by a specific intermediate variable. In the literature, there are two common definitions of direct effects; controlled and natural. When the intermediate variable and the outcome have common causes, neither the controlled nor the natural direct effect is identified. Cai et al. (Biometrics 2007; 64(3):695-701) derived bounds for the controlled direct effect under a set of hierarchical assumptions. In this paper we derive bounds on the natural direct effect under the same assumptions.
在流行病学研究中，我们常常希望了解暴露因素对结局的直接效应，即不由特定中间变量传递的效应。在文献中，直接效应有两种常见定义：受控直接效应和自然直接效应。当中间变量和结局存在共同原因时，受控直接效应和自然直接效应均无法识别。蔡等人（《生物统计学》2007年；64(3):695 - 701）在一组分层假设下推导了受控直接效应的界值。在本文中，我们在相同假设下推导了自然直接效应的界值。
