McGue Matt, Osler Merete, Christensen Kaare
Department of Psychology, University of Minnesota, Minneapolis Institute of Public Health, University of Southern Denmark, Odense, Denmark
Institute of Public Health, University of Southern Denmark, Odense, Denmark Research Center for Prevention and Health, Glostrup Hospital, Glostrup, Denmark;
Perspect Psychol Sci. 2010 Sep;5(5):546-56. doi: 10.1177/1745691610383511.
Valid causal inference is central to progress in theoretical and applied psychology. Although the randomized experiment is widely considered the gold standard for determining whether a given exposure increases the likelihood of some specified outcome, experiments are not always feasible and in some cases can result in biased estimates of causal effects. Alternatively, standard observational approaches are limited by the possibility of confounding, reverse causation, and the nonrandom distribution of exposure (i.e., selection). We describe the counterfactual model of causation and apply it to the challenges of causal inference in observational research, with a particular focus on aging. We argue that the study of twin pairs discordant on exposure, and in particular discordant monozygotic twins, provides a useful analog to the idealized counterfactual design. A review of discordant-twin studies in aging reveals that they are consistent with, but do not unambiguously establish, a causal effect of lifestyle factors on important late-life outcomes. Nonetheless, the existing studies are few in number and have clear limitations that have not always been considered in interpreting their results. It is concluded that twin researchers could make greater use of the discordant-twin design as one approach to strengthen causal inferences in observational research.
有效的因果推断是理论心理学和应用心理学取得进展的核心。尽管随机实验被广泛认为是确定给定暴露是否会增加某些特定结果发生可能性的黄金标准，但实验并不总是可行的，而且在某些情况下可能会导致因果效应的偏差估计。另外，标准的观察性方法受到混杂、反向因果关系以及暴露的非随机分布（即选择）可能性的限制。我们描述了因果关系的反事实模型，并将其应用于观察性研究中的因果推断挑战，特别关注衰老问题。我们认为，对暴露情况不一致的双胞胎对，尤其是不一致的同卵双胞胎进行研究，为理想化的反事实设计提供了有用的类比。对衰老领域中不一致双胞胎研究的综述表明，这些研究与生活方式因素对重要晚年结局的因果效应一致，但并未明确证实这一点。尽管如此，现有研究数量较少，且存在明显局限性，在解释其结果时并非总能考虑到这些局限性。得出的结论是，双胞胎研究人员可以更多地利用不一致双胞胎设计，作为加强观察性研究中因果推断的一种方法。
